The child's social development during the second half dozen years of his life is marked by important differences in the stability, intimacy, and strength of his friendships, as well as in the character of his play and other interests. Companionship is not so largely determined by propinquity as in the earlier years when the child's range of getting about was narrowly limited to his immediate small neighborhood. Children of similar chronological and mental ages, of similar developmental ages, having a community of interests and common activities, tend to be companions. With the increased experience, mental ability, and, general maturity resulting from age, lines of interest tend to become better defined. All of these conditions mean that his personality is developing and that his patterns of behavior are becoming more definite. Accordingly, the selection of companions becomes less childish and more mature as first puberty, then adolescence, maturity, and middle age approach. In later childhood, however, proximity may still be a factor, because it does provide opportunities for acquaintanceship and more or less intimate understanding. Thus, studies of gangs show that living in the same neighborhood (common environment) and being in the same grade at school are basic conditions underlying the forming of gangs. Other studies seem to show that children prefer as friends those who are quiet, self-controlled, "smart," good in their lessons, strong, and "not silly." At least, these are some of the qualities which they say they prefer.
Factors in the Formation of Groups
During the first four or five years of the child's life the factors that induce the child's contacts with others and the formation of groups seem to be helplessness and need, companionship in play, and common interests in toys or other objects. These earliest groups usually have two members, while later on larger groups are formed. During the years from six to twelve, common interests and activities, similarity in chronological, mental, and developmental ages, are factors underlying the formation of groups. Such groups are more stable and lasting than the rapidly shifting groupings of the pre-school years. Various environmental factors also may be influential, such as living in a certain neighborhood close to some other groups whose activities are well known. At about the eighth to tenth years boys and girls frequently form clubs or gangs of one sort or another. Many of these are short-lived. A name, membership dues, a time and place of meeting, a list of members, and no very definite specified purposes, are common characteristics of many clubs at this age. We have studied many of them among public-school children, ages eight to fourteen. Girls' clubs are common at these ages and are very transitory and short-lived. Boys' clubs seem to be more definite in their objectives and more lasting. It may be that boys feel a keener need for such social groupings. The intimacy, loyalty, and solidarity in some of these groups are truly remarkable, as various detailed accounts of them have shown.
Community feeling, however, seems to be slow in developing. Tattling is found in the earlier school years. Identification of one's self with the group in such a vital way as to regard group success as highly satisfying is also slow in developing. Doing things for the good of the group, as in teamwork, develops gradually. Even several years after the child begins school it may have little motivating power in child behavior. Anyone organizing a baseball team of ten-year-old boys is not likely to have any scarcity of candidates for catching, pitching, first base, and short stop, but he will lack fielders.
Tuesday, March 25, 2008
Social Concepts of Children Six to Twelve Years of Age
The child's ability to identify facial expressions representing certain emotional states improves with age, as has been noted already. Actual objects may be identified as to use by the age of from two and a half to three and a half years. Simple words such as ball, hat, and stove can be defined by the age of five. The understanding of abstract words is a later development. Only at age twelve can the average child define two of four words such as constant, courage, charity, and defend.
Such concepts as playing fairly, being kind, helping others, and the like have their beginnings in the early pre-school years. Normally they are well developed before the advent of puberty. We must not conclude, however, that having an accurate knowledge of certain social concepts insures their operation in the daily lives of children. Often a notable discrepancy is found between knowledge and overt behavior.
Social Contacts and Adjustment of Later Childhood
Entrance upon school, provides stimuli to many social reactions. The first reactions of children to school are not necessarily complete indications of their social development. Thus, a one-year study of forty seven-year-old boys just entering school showed that thirteen were confident, sixteen indifferent, and eleven were shy. The early over-submissiveness to the teacher's authority tended to disappear during the first six weeks. Considerable disobedience was found, even though the authority of the teacher was clearly recognized and not disputed. Often difficulties arose because the boys did not know exactly what was expected of them, or because they misunderstood the meaning of a given command.
Various schemes for classifying children's social contacts have been devised. One type of classification divides social contacts into, five principal classes. (1) Protective contacts are those in which the shy and submissive or uncertain child attaches himself to the selfassertive. If anything happens to break up the association, the timid child seeks someone else to whom he may attach himself. (2) Social contacts may reveal a certain kind of devotion in which a beloved or popular child is the center of a group, not because of any marked leadership, but because of his gentle, friendly, attractive ways which make so many children like him. (3) Social contacts also may be those of the "leader." (4) Sometimes they show the "despot." (5) A fifth type is that of the child who is socially unsuccessful. Social contacts, characterized as a despotism, tend to diminish by the time children finish kindergarten or enter first grade. Force as a controlling element becomes socially unacceptable and many children give it up. The socially unsuccessful child often is the one who has some physical defect or who has been badly neglected, having torn, dirty, or ill-fitting clothing. Often such children become trouble-makers in school. By the beginning of the school years the range of the child's social reactions is vast indeed. By the age of twelve years, nearly every type of social response has appeared, although the range and complexity of the situations evoking them are far from the scope shown in later adolescence or adulthood.
Such concepts as playing fairly, being kind, helping others, and the like have their beginnings in the early pre-school years. Normally they are well developed before the advent of puberty. We must not conclude, however, that having an accurate knowledge of certain social concepts insures their operation in the daily lives of children. Often a notable discrepancy is found between knowledge and overt behavior.
Social Contacts and Adjustment of Later Childhood
Entrance upon school, provides stimuli to many social reactions. The first reactions of children to school are not necessarily complete indications of their social development. Thus, a one-year study of forty seven-year-old boys just entering school showed that thirteen were confident, sixteen indifferent, and eleven were shy. The early over-submissiveness to the teacher's authority tended to disappear during the first six weeks. Considerable disobedience was found, even though the authority of the teacher was clearly recognized and not disputed. Often difficulties arose because the boys did not know exactly what was expected of them, or because they misunderstood the meaning of a given command.
Various schemes for classifying children's social contacts have been devised. One type of classification divides social contacts into, five principal classes. (1) Protective contacts are those in which the shy and submissive or uncertain child attaches himself to the selfassertive. If anything happens to break up the association, the timid child seeks someone else to whom he may attach himself. (2) Social contacts may reveal a certain kind of devotion in which a beloved or popular child is the center of a group, not because of any marked leadership, but because of his gentle, friendly, attractive ways which make so many children like him. (3) Social contacts also may be those of the "leader." (4) Sometimes they show the "despot." (5) A fifth type is that of the child who is socially unsuccessful. Social contacts, characterized as a despotism, tend to diminish by the time children finish kindergarten or enter first grade. Force as a controlling element becomes socially unacceptable and many children give it up. The socially unsuccessful child often is the one who has some physical defect or who has been badly neglected, having torn, dirty, or ill-fitting clothing. Often such children become trouble-makers in school. By the beginning of the school years the range of the child's social reactions is vast indeed. By the age of twelve years, nearly every type of social response has appeared, although the range and complexity of the situations evoking them are far from the scope shown in later adolescence or adulthood.
The Relationship of Language to Social Development
The child's social development is profoundly influenced by his language development. Through language he not only expresses his thoughts and feelings to others, but he understands something of their thoughts, feelings, and desires. Language thus enables the child to understand others and gives him a ready means of influencing their behavior. It helps him in the development of social concepts of more complex and abstract nature. Anyone can observe the great amount of talk or conversation in a group of pre-school children at play, even though much of it may relate to the speaker and his exploits. At the earliest pre-school age, language is not the child's usual means of initiating contacts with others, nor is it the most common means at the age of five or six. Some object or activity of common interest is much more likely to be used to bring about social contacts. Only in later years of childhood and more particularly in adolescence does language hold a relatively important place in making social contacts. It is, however, a very important means of maintaining them, even during the pre-school years. On countless occasions parents and teachers have observed children trying to hold attention by asking questions, by telling about events, or by other conversational efforts.
Social Attitudes of Pre-School Children
Socially indifferent children are rare, however, at the age of four or five years. A few may be observed who seem almost lacking in social perception, and whose behavior is very little influenced by the activities of others. Mental ability has some effect on this characteristic. We have seen feebleminded children ten to twelve years of age who seemed to give no sign of being aware of the presence or activity of other persons. At the very bottom of the scale of intelligence there are always children whose social behavior is practically zero.
Social dependence or social independence may be quite marked in pre-school children, although most youngsters possess this trait in some degree intermediate between the extremes. The social dependence or independence of a child is probably the result of his training, and experience more than of any other factors. We have observed many children in kindergartens of city public schools and in free kindergartens maintained by charitable and philanthropic organizations and have seen timid children lose much of their timidity in groups and develop leadership in group activities. The child on whom satisfactions are bestowed because of his submissiveness, who is threatened into frequent yielding, or who is given no opportunities for spontaneous and voluntary action, is likely to be dependent. When these circumstances operate in the opposite manner, independence results. Since most children receive these stimulations in an intermediate degree, they are neither strikingly dependent nor independent, or else they show these characteristics differently in various particular situations.
Social Attitudes of Pre-School Children
Socially indifferent children are rare, however, at the age of four or five years. A few may be observed who seem almost lacking in social perception, and whose behavior is very little influenced by the activities of others. Mental ability has some effect on this characteristic. We have seen feebleminded children ten to twelve years of age who seemed to give no sign of being aware of the presence or activity of other persons. At the very bottom of the scale of intelligence there are always children whose social behavior is practically zero.
Social dependence or social independence may be quite marked in pre-school children, although most youngsters possess this trait in some degree intermediate between the extremes. The social dependence or independence of a child is probably the result of his training, and experience more than of any other factors. We have observed many children in kindergartens of city public schools and in free kindergartens maintained by charitable and philanthropic organizations and have seen timid children lose much of their timidity in groups and develop leadership in group activities. The child on whom satisfactions are bestowed because of his submissiveness, who is threatened into frequent yielding, or who is given no opportunities for spontaneous and voluntary action, is likely to be dependent. When these circumstances operate in the opposite manner, independence results. Since most children receive these stimulations in an intermediate degree, they are neither strikingly dependent nor independent, or else they show these characteristics differently in various particular situations.
The Formation of Friendships During the First Five Years
As nearly as can be told from the available evidence, children are naturally neither friendly nor unfriendly. Friendliness is the outcome of environmental forces, as is also unfriendliness. The meaning of anything to a child is the result of his experiences with it, determined by what it does to or for him, and by what he can do to it. In this respect, people are merely objects in the child's environment. What they mean to him follows directly from his experiences with them. Under one kind of environment he will become friendly, under another, unfriendly. The majority of children spend their early years in homes in which people care for their needs. They are fed, clothed, and comforted, their pain is relieved, and many other things that make for their well-being, happiness, and contentment are performed. Accordingly, we would expect the majority of young children to be friendly rather than unfriendly. A study of two-year-olds shows this to be the case. They were brought it into a small playroom two at a time, each child being paired with each other child of the group, and their responses were recorded. The results showed that friendliness was far more common than unfriendliness -- in terms of score, 89.5 and 20.5, respectively. If children's early experiences with people were marked by abuse, pain, and the like, unfriendliness undoubtedly would be developed instead.
Obviously, the factors which further the formation of friendships in childhood are those which satisfy, please, comfort, or help the child in some way. Factors which hinder or prevent the formation of friendships are those which irritate, anger, pain, or otherwise displease the child. A very long list of specific conditions tending to develop friendliness could be given, and another list conducive to unfriendliness could be set forth. The close contacts incident to living in the same family may lead to bitter hatred or warm affection. If children interfere with each other in any way continually for a considerable period of time, they are likely to become unfriendly and jealous of each other. With young children proximity is a very common factor in friendship and companionship. The child cannot go far from home. Accordingly, he makes friends with children near at hand. Mere propinquity may not be enough to develop companionship, but if the children are near the same age, they are likely to have enough community of interest to become friends. At all ages, it would seem, community of interest is a very important factor conditioning friendship. Children who like to do the same things are likely to be friends, if they have the opportunity to be together so as to discuss their common likes, provided, of course, that other conditions giving rise to friction are absent.
When pre-school children are allowed to form groups freely, sex plays less of a part than with older children who tend to group themselves according to sex. Children, if left to themselves, form groups largely upon the basis of acceptable behavior and ability to enter into the group activities. When race, color, poverty, or riches are factors in the formation of groups of pre-school children, we may be sure that home pressure or the influence of other adults is likely to be responsible for the social discrimination displayed. Such factors otherwise have little meaning or value for the child of four or five years.
A youngster of three or four years of age often forms a strong attachment for some other child and seeks to be with him as much as possible. Such little chums may be seen going home together from nursery school or kindergarten. They are much together at school and out of school, if opportunity can be found. Such friendships may last for several months, although more commonly they last only a few days or weeks. We have observed many of these among kindergarten children four or five years old. Usually two children are chums. Less frequently three may be chums for a while. In one case we observed three boys who became great chums in kindergarten at the age of five. Their friendship continued through the first and second grades, until one of the boys moved to another city. We also have seen a few cases of three girls being chums in kindergarten for a short time. We have seen the close friendship between two boys or two girls lasting for some time in several cases through kindergarten and several years thereafter. We would expect such cases to be found, because some of the children, having the traits which make for friendship, are likely to develop in ways which will continue their being chums. On the whole, however, pre-school children do not maintain such chumships for a long period of time, as nurseryschool and kindergarten teachers often have observed.
Obviously, the factors which further the formation of friendships in childhood are those which satisfy, please, comfort, or help the child in some way. Factors which hinder or prevent the formation of friendships are those which irritate, anger, pain, or otherwise displease the child. A very long list of specific conditions tending to develop friendliness could be given, and another list conducive to unfriendliness could be set forth. The close contacts incident to living in the same family may lead to bitter hatred or warm affection. If children interfere with each other in any way continually for a considerable period of time, they are likely to become unfriendly and jealous of each other. With young children proximity is a very common factor in friendship and companionship. The child cannot go far from home. Accordingly, he makes friends with children near at hand. Mere propinquity may not be enough to develop companionship, but if the children are near the same age, they are likely to have enough community of interest to become friends. At all ages, it would seem, community of interest is a very important factor conditioning friendship. Children who like to do the same things are likely to be friends, if they have the opportunity to be together so as to discuss their common likes, provided, of course, that other conditions giving rise to friction are absent.
When pre-school children are allowed to form groups freely, sex plays less of a part than with older children who tend to group themselves according to sex. Children, if left to themselves, form groups largely upon the basis of acceptable behavior and ability to enter into the group activities. When race, color, poverty, or riches are factors in the formation of groups of pre-school children, we may be sure that home pressure or the influence of other adults is likely to be responsible for the social discrimination displayed. Such factors otherwise have little meaning or value for the child of four or five years.
A youngster of three or four years of age often forms a strong attachment for some other child and seeks to be with him as much as possible. Such little chums may be seen going home together from nursery school or kindergarten. They are much together at school and out of school, if opportunity can be found. Such friendships may last for several months, although more commonly they last only a few days or weeks. We have observed many of these among kindergarten children four or five years old. Usually two children are chums. Less frequently three may be chums for a while. In one case we observed three boys who became great chums in kindergarten at the age of five. Their friendship continued through the first and second grades, until one of the boys moved to another city. We also have seen a few cases of three girls being chums in kindergarten for a short time. We have seen the close friendship between two boys or two girls lasting for some time in several cases through kindergarten and several years thereafter. We would expect such cases to be found, because some of the children, having the traits which make for friendship, are likely to develop in ways which will continue their being chums. On the whole, however, pre-school children do not maintain such chumships for a long period of time, as nurseryschool and kindergarten teachers often have observed.
Interpretation of Facial Expressions
The early recognition of certain facial and vocal expressions, such as smiling or angry looks and kind or scolding tones, found among infants from the fifth month on, is an important step in understanding the behavior of human beings. We find children showing greater skill along this line as they get older.
More than 70 per cent of the kindergarten children recognized laughter, whereas less than 50 per cent of them recognized fear, anger, or pain. By the age of seven years more than half recognized anger, by eleven, more than half recognized surprise. The course of development may be seen also in the fact that the average number of photographs correctly named was 1.5 at the age of three years, and, nearly four and one-half at the age of eleven. Of course, this test is somewhat artificial because actual facial expressions are mobile or changing rather than fixed or static. Accordingly, we must not conclude that children cannot recognize fear, anger, and pain in a familiar person's behavior until the ages shown in the foregoing study. The addition of vocal expressions is a distinct supplementary aid to the child in identifying the emotional states of a familiar person.
Laughter and Crying of the Pre-School Child
The laughter and crying of children under five years of age have significance in studying their social development. Apparently, 8 more of the two-year-old's laughter takes place when he is unaware of another child's presence and is playing by himself. At a later age, however, the most laughter seems to occur when children are in social contact with other children. Boys seem to laugh most and cry most when with boys. In the latter case, the teasing or amusing nature of the social contact may be a contributing factor.
More than 70 per cent of the kindergarten children recognized laughter, whereas less than 50 per cent of them recognized fear, anger, or pain. By the age of seven years more than half recognized anger, by eleven, more than half recognized surprise. The course of development may be seen also in the fact that the average number of photographs correctly named was 1.5 at the age of three years, and, nearly four and one-half at the age of eleven. Of course, this test is somewhat artificial because actual facial expressions are mobile or changing rather than fixed or static. Accordingly, we must not conclude that children cannot recognize fear, anger, and pain in a familiar person's behavior until the ages shown in the foregoing study. The addition of vocal expressions is a distinct supplementary aid to the child in identifying the emotional states of a familiar person.
Laughter and Crying of the Pre-School Child
The laughter and crying of children under five years of age have significance in studying their social development. Apparently, 8 more of the two-year-old's laughter takes place when he is unaware of another child's presence and is playing by himself. At a later age, however, the most laughter seems to occur when children are in social contact with other children. Boys seem to laugh most and cry most when with boys. In the latter case, the teasing or amusing nature of the social contact may be a contributing factor.
Responses of Infants to Other Infants
AGE IN MONTHS
Observes other child 4 to 5
Smiles at other child 4 to 5
Cries if other child receives attention 8 to 9
Offers toy to other child 8 to 9
"Lalls" to other child 8 to 9
Imitates movements of another child 9 to 10
Opposes toy being taken away 9 to 10
Organized play activity 10 to 11
Strives for attention by means of "lalling" 10 to 11
Ill-humor if another child moves away 10 to 11
Setting aside toy and turning toward another child 11 to 12
If they noticed them, it was with no interest or emotion. Even the others' movements were of no interest. Such infants played, moved about, cooed, and smiled without any interest or regard for the presence of other infants who were near. Such behavior may be regarded as exhibiting social blindness. The infants who were not socially "blind," that is, those who paid attention to the behavior of others, exhibited varying degrees of independence in social relations. At one extreme some showed a high degree of social dependence. They were much influenced by the presence and activities of other infants. At the other extreme were infants who, equally aware of the presence and activities of others, still showed a great deal of social independence. The socially dependent infant's behavior seemed to be conditioned largely by that of another. He usually copied it or he may merely have watched it. Or if he was not so timid or if his responses were not so readily inhibited, he might go through his little repertory of stunts trying to arouse or please the other. The socially independent infant was aware of the presence of the other and responded to him and his behavior, but did not seem to be dependent upon him. He played with him but was clearly the leader, not being afraid of or intimidated by the other. Children from six months to eighteen months of age possess these characteristics in greater or less degree. Bühler believed that they show them without reference to previous contacts with others, to their being only children, to the home conditions, or to nationality. We may have here early evidence of dominance and submission.
Any reference to infants as socially dependent or socially independent, however, must not be applied too rigidly. We must not think of all children who are not "socially blind" as belonging at either of these other two extremes. Some do belong to the first class and some to the second. Many, however, seem to fall into groupings between the extremes, especially as they pass from infancy to the pre-school and school years. As characterizations of general social attitudes of individuals, Bühler's classes are suggestive and valuable because they throw into clear relief important considerations in the social development of the child. No scheme of classifying children into two or three "types" is satisfactory, however, as is seen in connection with the discussion of child personalities.
Observes other child 4 to 5
Smiles at other child 4 to 5
Cries if other child receives attention 8 to 9
Offers toy to other child 8 to 9
"Lalls" to other child 8 to 9
Imitates movements of another child 9 to 10
Opposes toy being taken away 9 to 10
Organized play activity 10 to 11
Strives for attention by means of "lalling" 10 to 11
Ill-humor if another child moves away 10 to 11
Setting aside toy and turning toward another child 11 to 12
If they noticed them, it was with no interest or emotion. Even the others' movements were of no interest. Such infants played, moved about, cooed, and smiled without any interest or regard for the presence of other infants who were near. Such behavior may be regarded as exhibiting social blindness. The infants who were not socially "blind," that is, those who paid attention to the behavior of others, exhibited varying degrees of independence in social relations. At one extreme some showed a high degree of social dependence. They were much influenced by the presence and activities of other infants. At the other extreme were infants who, equally aware of the presence and activities of others, still showed a great deal of social independence. The socially dependent infant's behavior seemed to be conditioned largely by that of another. He usually copied it or he may merely have watched it. Or if he was not so timid or if his responses were not so readily inhibited, he might go through his little repertory of stunts trying to arouse or please the other. The socially independent infant was aware of the presence of the other and responded to him and his behavior, but did not seem to be dependent upon him. He played with him but was clearly the leader, not being afraid of or intimidated by the other. Children from six months to eighteen months of age possess these characteristics in greater or less degree. Bühler believed that they show them without reference to previous contacts with others, to their being only children, to the home conditions, or to nationality. We may have here early evidence of dominance and submission.
Any reference to infants as socially dependent or socially independent, however, must not be applied too rigidly. We must not think of all children who are not "socially blind" as belonging at either of these other two extremes. Some do belong to the first class and some to the second. Many, however, seem to fall into groupings between the extremes, especially as they pass from infancy to the pre-school and school years. As characterizations of general social attitudes of individuals, Bühler's classes are suggestive and valuable because they throw into clear relief important considerations in the social development of the child. No scheme of classifying children into two or three "types" is satisfactory, however, as is seen in connection with the discussion of child personalities.
Responses of Infants to Adults
AGE IN MONTHS
Returns glance of adult with smiling 1 to 2
Is quieted by touching 1 to 2
Cries when adult who was attending him leaves 2 to 3
Smiles back at adult 2 to 3
Disturbed when approached 2 to 3
Returns approaching glance with "lalling" 3 to 4
Displeasure when loses glance of adult 3 to 4
Quieted by caressing 4 to 5
Disturbed by the sight of people 4 to 5
Striving for attention by "lalling" 7 to 8
Stretches out hands toward adults 7 to 8
Cries when adult stops talking 7 to 8
Strives for attention by movements 8 to 9
Pulls on the clothes of adult 9 to 10
Offers adult an object 9 to 10
Imitates movements of adult with a plaything 9 to 10
Organized play activity 10 to 11
Returns glance of adult with smiling 1 to 2
Is quieted by touching 1 to 2
Cries when adult who was attending him leaves 2 to 3
Smiles back at adult 2 to 3
Disturbed when approached 2 to 3
Returns approaching glance with "lalling" 3 to 4
Displeasure when loses glance of adult 3 to 4
Quieted by caressing 4 to 5
Disturbed by the sight of people 4 to 5
Striving for attention by "lalling" 7 to 8
Stretches out hands toward adults 7 to 8
Cries when adult stops talking 7 to 8
Strives for attention by movements 8 to 9
Pulls on the clothes of adult 9 to 10
Offers adult an object 9 to 10
Imitates movements of adult with a plaything 9 to 10
Organized play activity 10 to 11
Other Social Responses During Infancy
The infant makes other responses which are indicative of very simple social behavior. Upon the approach of a familiar person the fourmonths-old infant very often raises his arms and stiffens his body slightly in anticipation of being lifted. He also shows some delight upon the approach of the familiar person. Of course, some infants make these responses earlier, but by the age of four months the majority are likely to do so. Infants of this age have some remembrance of events and often seem to look for a face that has disappeared, gazing for some little time toward the place they last saw it. Sometimes infants of four months chuckle or laugh when familiar persons resort to certain playful activities. A month or two later many infants show greater development of social behavior, and respond to other social stimulations. With the development of motor skill, adaptive behavior, attention, discrimination, and language, the infant increases not only the scope of his responses to the presence and activities of other persons, but also the number and types of social situations to which he can respond.
How Infants Respond to the Presence of Other Infants
Babies at four and five months of age frequently seem to be unaware of each other's presence, even though near each other. By the age of six months, however, they actively look around and attract each other's attention. Thus, the infant of six or seven months may touch another one who is near, or he may coo, or hinder the other's activities in some way. We have observed a few babies of five to eight months, placing them two at a time near each other on a bed or couch. The older ones showed distinct evidence of being aware of the presence of each other. Thus, an eight-months-old infant when placed near one of five months reached out and stroked the younger one and then took hold of her arm, cooing, gurgling, and smiling. The younger infant had given no previous sign of seeing the other and was cooing contentedly. Upon being touched, she stopped cooing, turned her head, and looked at the other baby. She did not, however, put out her hand and try to touch the older one. Responses to the presence and activities of adults and older children are observable at an earlier age than are responses to other infants of about the same age, undoubtedly because the former provide more adequate stimuli.
How Infants Respond to the Presence of Other Infants
Babies at four and five months of age frequently seem to be unaware of each other's presence, even though near each other. By the age of six months, however, they actively look around and attract each other's attention. Thus, the infant of six or seven months may touch another one who is near, or he may coo, or hinder the other's activities in some way. We have observed a few babies of five to eight months, placing them two at a time near each other on a bed or couch. The older ones showed distinct evidence of being aware of the presence of each other. Thus, an eight-months-old infant when placed near one of five months reached out and stroked the younger one and then took hold of her arm, cooing, gurgling, and smiling. The younger infant had given no previous sign of seeing the other and was cooing contentedly. Upon being touched, she stopped cooing, turned her head, and looked at the other baby. She did not, however, put out her hand and try to touch the older one. Responses to the presence and activities of adults and older children are observable at an earlier age than are responses to other infants of about the same age, undoubtedly because the former provide more adequate stimuli.
Earliest Social Stimulations and Responses
Since normal infants become able to perceive objects in the environment at about the same time and since all have the fundamental experiences basic to social behavior, a typical sequence of the development of social responses can be described. Some conditioned social responses have been reported during the first month of life. Infants of this age sometimes stop crying when someone speaks, when someone enters the room, or even at the sight of a human face. Although these reactions seem to be responses to the presence of people, caution is necessary in interpreting them in individual instances. Very young infants often stop crying when any stimulus arouses their attention. If something touches him, if any noise or movement occurs, or if he merely relieves his own discomfort by turning to a less cramped position, the same response may be made. Some responses of infants to persons, then, are really social, while in other cases the infant reacts to the person only as a mechanical agent.
By the second month, social responses to persons are more clearly distinguishable. At the age of two full months, many infants will turn the head and eyes toward the sound of a human voice. These responses, of course, do not develop because of any inner social tendency, but are evidences of learned behavior.
The Recognition of Facial and Vocal Expressions
During the first two months of postnatal life the infant's smile at the presence of another human being is not dependent upon the latter's facial expression or tone of voice. The young human is not yet able to differentiate such relatively simple things as smiling and angry facial expressions, or kind and scolding words and tone. If a person bends over the crib of a two-monthsold infant and has a "smiling countenance," the infant may smile in return. But if the adult has an angry expression, the infant also may smile. The, infant even at the age of three or four months probably is unable to differentiate kind and angry looks, tones or gestures, although exceptions occur. From the close of the fourth month, however, infants show distinct signs of differentiating expressions and by the fifth month may cry at the scolding voice and threatening gesture. The child by this time has developed his powers of attention and observation to such an extent that he can watch the face and note any changes in its details. He also is capable of discriminating differences in tone of voice. Perhaps even more important is the fact that he has now learned that kindly expressions typically accompany satisfying ministrations to his needs, while harsh ones imply neglect or even painful punishment. Before the end of the first year he has made a great deal of progress in understanding vocal and facial expressions.
By the second month, social responses to persons are more clearly distinguishable. At the age of two full months, many infants will turn the head and eyes toward the sound of a human voice. These responses, of course, do not develop because of any inner social tendency, but are evidences of learned behavior.
The Recognition of Facial and Vocal Expressions
During the first two months of postnatal life the infant's smile at the presence of another human being is not dependent upon the latter's facial expression or tone of voice. The young human is not yet able to differentiate such relatively simple things as smiling and angry facial expressions, or kind and scolding words and tone. If a person bends over the crib of a two-monthsold infant and has a "smiling countenance," the infant may smile in return. But if the adult has an angry expression, the infant also may smile. The, infant even at the age of three or four months probably is unable to differentiate kind and angry looks, tones or gestures, although exceptions occur. From the close of the fourth month, however, infants show distinct signs of differentiating expressions and by the fifth month may cry at the scolding voice and threatening gesture. The child by this time has developed his powers of attention and observation to such an extent that he can watch the face and note any changes in its details. He also is capable of discriminating differences in tone of voice. Perhaps even more important is the fact that he has now learned that kindly expressions typically accompany satisfying ministrations to his needs, while harsh ones imply neglect or even painful punishment. Before the end of the first year he has made a great deal of progress in understanding vocal and facial expressions.
The Learning of Social Behavior
The newborn child is neither a social nor an unsocial being. He is a highly complex organism equipped to respond to certain sorts of stimulations, as has been seen throughout the discussion of infant behavior. He also possesses a high degree of modifiability and significant potentialities for future growth and development. How soon after birth, then, does the child first show evidences of social behavior, of responding to the presence or activities of other persons? What are some of his earliest social responses? What particular kinds of stimulations evoke them? How do infants respond to the presence of other infants? What development of social behavior occurs during infancy and the pre-school years? During the years from six to twelve? What are the causes and significance of conflicts between children? What factors influence the child's social development? What is the significance of social approval, self-assertion, language development, gregariousness and other elements upon the development of social behavior during the first dozen years of life? These are some of the important problems whose answers now concern us.
Although the infant is non-social at birth, he cannot remain so for a very long time. He lives in a society and is constantly dependent upon other people for his welfare and comforts. Accordingly, the infant soon learns to make responses to other persons. As he grows from infancy to childhood, these social adjustments become even more evident.
The Learning of Social Behavior
The earliest social behavior of infants arises from the care and handling given to them by, adults. When a baby is fed, dried, kept warm or petted, he responds by behavior that may be taken to indicate satisfaction. If he is restless or crying, this agitated behavior ceases. With a little greater maturity, positive evidences of pleasure are apparent in the forms of smiling, gurgling, cooing, laughing, and reaching with the arms. Fundamentally, all social behavior is based on these responses to the satisfaction of the infant's bodily needs.
During the early months of life, learning takes place by which these reactions come to be made to persons, rather than only to the actual bodily stimulations. This learning is an example of the operation of the conditioned reaction. Since the mother or nurse or some other adult is always present when these ameliorative satisfactions are administered, the sight, sound, or other symbol of these persons becomes capable of evoking the response. The beginning of social behavior in infants is dependent upon the development of their abilities of perception and discrimination and upon the occurrence of experiences through which they may learn.
Although the infant is non-social at birth, he cannot remain so for a very long time. He lives in a society and is constantly dependent upon other people for his welfare and comforts. Accordingly, the infant soon learns to make responses to other persons. As he grows from infancy to childhood, these social adjustments become even more evident.
The Learning of Social Behavior
The earliest social behavior of infants arises from the care and handling given to them by, adults. When a baby is fed, dried, kept warm or petted, he responds by behavior that may be taken to indicate satisfaction. If he is restless or crying, this agitated behavior ceases. With a little greater maturity, positive evidences of pleasure are apparent in the forms of smiling, gurgling, cooing, laughing, and reaching with the arms. Fundamentally, all social behavior is based on these responses to the satisfaction of the infant's bodily needs.
During the early months of life, learning takes place by which these reactions come to be made to persons, rather than only to the actual bodily stimulations. This learning is an example of the operation of the conditioned reaction. Since the mother or nurse or some other adult is always present when these ameliorative satisfactions are administered, the sight, sound, or other symbol of these persons becomes capable of evoking the response. The beginning of social behavior in infants is dependent upon the development of their abilities of perception and discrimination and upon the occurrence of experiences through which they may learn.
Children's Recreational and Social Interests
The play activities of children give valuable clues to the child's nature and needs. In infancy his interests are centered upon manipulating the simple toys and other objects in his hands -- squeezing, pushing, pulling, or striking them upon the table, crib, or high-chair, or attempting to put them in his mouth. The diffuse and random nature of such activities has been reported frequently. By the age of three or four years we find more varied play activities. Playing with toys in the sand pile, building houses with blocks, riding kiddie cars, playing with toy automobiles and wagons, playing house, playing train, playing with dolls, riding tricycle, etc., may be observed. At the age of five years play interests still center about games and activities which are largely individual and solitary, and do not require the participation or cooperation of other children. Jumping, climbing, running, sliding, digging, throwing, lifting, and rolling are whole-body activities performed without any motive of doing one's best or of doing better than someone else. The presence of another child may be resented, and if he has some plaything, a struggle for its possession may ensue.
Children at this age may play in small groups, but often they really are not playing in groups, they are merely near each other while playing. The directed play activities of the kindergarten often involve ring games, rhythmic movement, and singing games. The five-year-old is likely to enjoy construction work. If he is given some direction and if tools are available, he will try to make crude objects, using saw and hammer. Play interests at this age are characterized by the child's engaging in the activity from sheer enjoyment of it, and not to acquire any skill. With further increases of age, the nature of his play interests again changes. By the age of ten or eleven marked differences are seen. The free individual play activities without rules and competition have been displaced by games with rules and with some object or goal. Such games are likely to be largely competitive, with much rivalry in the case of boys. Interest centers on skill and excellence. The games run a definite course, that is, they have a beginning and come to an end. Little cooperation is found. In fact the adult who gets together a group of ten-year-old boys for a baseball or football team is likely to have a surplus of would-be pitchers, firstbasemen, quarterbacks, and centers, but a dearth of fielders and players who do not carry the ball. Emphasis upon speed, strength, and accuracy is characteristic of the play activities of the boy at ten. He is much interested in excelling the others in running, throwing, and the like. Using tools to make things, engaging in bicycle-riding, climbing trees, skating, swimming, camping out, and playing with various kinds of mechanical devices are also much enjoyed. Among girls of ten years, doll play has begun to decline and in the next three years will almost disappear. Playing with paper dolls, making clothes for dolls, participating in various kinds of table games, bicycle-riding, playing on the horizontal bar, house-keeping activities, puzzles, dancing, and dramatic games are common among girls of ten or eleven years.
A conspicuous change in recreational activities is suggested by the percentages of children, at each age up to fifteen, attending the movies, climbing trees, porches, and fences, riding bicycles, and playing marbles. At twelve years of age, two-thirds of the town boys and three-fifths of the town girls attend motion pictures. Nearly half of the eight- and nine-year-old town children also attend. These proportions are in distinct contrast with the smaller percentages who engage in climbing, play marbles, skip rope, etc.
The environment facilitates participation in some play activities and limits it in others, as we would expect. In all of these play problems is found the customary wide range of individual differences. Many play activities indicate the development of social interests. Girls' interests include social dancing, picnics, parties, and "dates," while boys' interests are in football, baseball, and basketball, all of which involve cooperation or teamwork.
Children at this age may play in small groups, but often they really are not playing in groups, they are merely near each other while playing. The directed play activities of the kindergarten often involve ring games, rhythmic movement, and singing games. The five-year-old is likely to enjoy construction work. If he is given some direction and if tools are available, he will try to make crude objects, using saw and hammer. Play interests at this age are characterized by the child's engaging in the activity from sheer enjoyment of it, and not to acquire any skill. With further increases of age, the nature of his play interests again changes. By the age of ten or eleven marked differences are seen. The free individual play activities without rules and competition have been displaced by games with rules and with some object or goal. Such games are likely to be largely competitive, with much rivalry in the case of boys. Interest centers on skill and excellence. The games run a definite course, that is, they have a beginning and come to an end. Little cooperation is found. In fact the adult who gets together a group of ten-year-old boys for a baseball or football team is likely to have a surplus of would-be pitchers, firstbasemen, quarterbacks, and centers, but a dearth of fielders and players who do not carry the ball. Emphasis upon speed, strength, and accuracy is characteristic of the play activities of the boy at ten. He is much interested in excelling the others in running, throwing, and the like. Using tools to make things, engaging in bicycle-riding, climbing trees, skating, swimming, camping out, and playing with various kinds of mechanical devices are also much enjoyed. Among girls of ten years, doll play has begun to decline and in the next three years will almost disappear. Playing with paper dolls, making clothes for dolls, participating in various kinds of table games, bicycle-riding, playing on the horizontal bar, house-keeping activities, puzzles, dancing, and dramatic games are common among girls of ten or eleven years.
A conspicuous change in recreational activities is suggested by the percentages of children, at each age up to fifteen, attending the movies, climbing trees, porches, and fences, riding bicycles, and playing marbles. At twelve years of age, two-thirds of the town boys and three-fifths of the town girls attend motion pictures. Nearly half of the eight- and nine-year-old town children also attend. These proportions are in distinct contrast with the smaller percentages who engage in climbing, play marbles, skip rope, etc.
The environment facilitates participation in some play activities and limits it in others, as we would expect. In all of these play problems is found the customary wide range of individual differences. Many play activities indicate the development of social interests. Girls' interests include social dancing, picnics, parties, and "dates," while boys' interests are in football, baseball, and basketball, all of which involve cooperation or teamwork.
Relation of Interest to Aptitude and Maturity
Investigation seems to lend support to the common-sense view that the child having ability in a given thing is likely to have more interest in it than he would in something in which he has little ability, and more interest in it than another child having less ability in it, other things in both cases being equal. Of course, if other things are not equal, they may overcome or outweigh the interest-producing effect of his ability. If, for example, a child does have considerable ability to do something but his experiences with it are loaded negatively with strong emotion, he may have little genuine interest in it. If an incompetent or disagreeable teacher introduces the child to some subject in school, he may have a resultant dislike for it, although he really may have considerable ability in it. Aside from the effect of such irrelevant, unfavorable elements, it seems reasonably well established that interest may be taken as some evidence of ability, provided the child actually has had some vital experience of the thing in question. We do not regard as evidence of interest a mere idle wish to do something, or a desire to do it which is the result of social pressure. The sense in which we use the term requires that it be genuine interest, as defined in the first part of this section -- active, objective, and personal.
Changes in interests are partly dependent upon maturation, as may be seen in the case of children's play interests. The ten-year-old's play activities are different from those of the four-year-old, not necessarily because he has had so much experience with them that he is surfeited by them, but rather because they were suited to a degree of development which he has long since passed. The reading interests of children also vary with age because of differences in, maturity, in intelligence, in outlook, and in experience. Undoubtedly, maturation is a factor in moulding children's interests along many other lines.
Changes in interests are partly dependent upon maturation, as may be seen in the case of children's play interests. The ten-year-old's play activities are different from those of the four-year-old, not necessarily because he has had so much experience with them that he is surfeited by them, but rather because they were suited to a degree of development which he has long since passed. The reading interests of children also vary with age because of differences in, maturity, in intelligence, in outlook, and in experience. Undoubtedly, maturation is a factor in moulding children's interests along many other lines.
Importance of Interests During Childhood
The value of many wholesome interests in the life of the child can hardly be overestimated. They bring him into vital contact with many activities. They provide a wealth of experiences because a child interested in an activity tends to engage in it. Sampling many lines of activity not only serves an exploratory function but also tends toward breadth of personality because of the wide range of experiences. Under these circumstances little danger exists of developing a narrow, one-sided personality. Out of a wealth of experiences may come a desirable breadth of appreciations. A wealth of interests also is important because it facilitates substitution in case of thwarting and helps the child avoid some conflicts which otherwise might arise. If he has many interests, he can, when blocked in respect to one of them, turn the more readily and with less strain from one interesting activity to some other one. Thus, many-sided interests have mental hygiene value not only during childhood, but also during adolescence and adult life.
As the years of childhood pass and the child comes into adolescence, we normally find some interests more permanent and of greater strength. Efficiency is dependent upon a few intense abiding interests which lead to centering attention and effort along some particular lines. Greatest achievement seems to be dependent upon the individual's having a strong abiding interest in the work he is doing. We need not, however, expect the child to have such a narrowed, intense, and relatively permanent interest along some line. He may show a very intense interest in some one thing for a short time and then turn with equal intensity to something else, or he may show much interest in several things simultaneously. During childhood cultivating and developing a wealth of wholesome interests should be an objective of child guidance and control by both parent and teacher.
As the years of childhood pass and the child comes into adolescence, we normally find some interests more permanent and of greater strength. Efficiency is dependent upon a few intense abiding interests which lead to centering attention and effort along some particular lines. Greatest achievement seems to be dependent upon the individual's having a strong abiding interest in the work he is doing. We need not, however, expect the child to have such a narrowed, intense, and relatively permanent interest along some line. He may show a very intense interest in some one thing for a short time and then turn with equal intensity to something else, or he may show much interest in several things simultaneously. During childhood cultivating and developing a wealth of wholesome interests should be an objective of child guidance and control by both parent and teacher.
What extent do interests motivate the child's behavior?
What is meant by interest? To what extent do interests motivate the child's behavior? Of what importance are they in his development? How closely are interests related to aptitude and maturity? What fundamental directions do the child's interests take? What are his recreational, social, intellectual, aesthetic, and vocational interests during the first dozen years of his life? What is the significance of his interests in motion pictures? What are the practical guides and effective laws and principles for developing wholesome interests? These are important questions for all who would understand the forces motivating children's behavior.
The Meaning of Interest. Interest has two diverse meanings in psychological usage. It means a condition or cause of attention; it also refers to the feeling of pleasure resulting from giving attention to something or from experiencing something. Webster defines interest as "excitement of feeling accompanying special attention to some object; concern; as, an interest in Botany." Thus, this term has been used to refer both to the cause and to the result of giving attention or of experiencing. Using the word in the first sense, we say the boy gets out his blocks because he is interested in building a house, or the little girl makes a doll dress because she is interested in having lots of clothes for her doll. Using it in the second sense, that of a resultant feeling of pleasure, we say the child is interested in playing at building a house or making doll dresses. These two meanings, while diverse, are closely related in the experiences and behavior of the child. Interest which is a result of the feeling of pleasure attendant upon some event or experience tends to condition the child in such a way that he later on does attend to that experience, object, or event because of the pleasure which resulted from previously experiencing or attending to it. This is merely saying that the result of a previous response may be, and frequently is, a present cause of repeating that response. Similarly, a present result may be a future cause. At any rate, interests are motives and often have very strong activating influence on the child's behavior.
Genuine interest is the accompaniment of the identification, through action, of the self with some object or idea, because of the necessity of that object or idea for the maintenance of a self-initiated activity. Effort, in the sense in which it may be opposed to interest, implies a separation between the self and the fact to be mastered or task to be performed, and sets up an habitual division of activities. Externally, we have mechanical habits with no mental end or value. Internally, we have random energy or mind-wandering, a sequence of ideas with no end at all, because they are not brought to a focus in action. Interest, in the sense in which it is opposed to effort, means simply an excitation of the sense organ to give pleasure, resulting in strain on one side and listlessness on the other.
Genuine interest is active, projective, or propulsive, is objective in that it does not end simply in itself, as some feelings may, but involves some object of regard, and is personal, signifying direct concern. The emotional side of interest is quite as significant as its active and objective sides.
The Meaning of Interest. Interest has two diverse meanings in psychological usage. It means a condition or cause of attention; it also refers to the feeling of pleasure resulting from giving attention to something or from experiencing something. Webster defines interest as "excitement of feeling accompanying special attention to some object; concern; as, an interest in Botany." Thus, this term has been used to refer both to the cause and to the result of giving attention or of experiencing. Using the word in the first sense, we say the boy gets out his blocks because he is interested in building a house, or the little girl makes a doll dress because she is interested in having lots of clothes for her doll. Using it in the second sense, that of a resultant feeling of pleasure, we say the child is interested in playing at building a house or making doll dresses. These two meanings, while diverse, are closely related in the experiences and behavior of the child. Interest which is a result of the feeling of pleasure attendant upon some event or experience tends to condition the child in such a way that he later on does attend to that experience, object, or event because of the pleasure which resulted from previously experiencing or attending to it. This is merely saying that the result of a previous response may be, and frequently is, a present cause of repeating that response. Similarly, a present result may be a future cause. At any rate, interests are motives and often have very strong activating influence on the child's behavior.
Genuine interest is the accompaniment of the identification, through action, of the self with some object or idea, because of the necessity of that object or idea for the maintenance of a self-initiated activity. Effort, in the sense in which it may be opposed to interest, implies a separation between the self and the fact to be mastered or task to be performed, and sets up an habitual division of activities. Externally, we have mechanical habits with no mental end or value. Internally, we have random energy or mind-wandering, a sequence of ideas with no end at all, because they are not brought to a focus in action. Interest, in the sense in which it is opposed to effort, means simply an excitation of the sense organ to give pleasure, resulting in strain on one side and listlessness on the other.
Genuine interest is active, projective, or propulsive, is objective in that it does not end simply in itself, as some feelings may, but involves some object of regard, and is personal, signifying direct concern. The emotional side of interest is quite as significant as its active and objective sides.
Habits, Purposes, and Ideals as Motives
Other complex learned motives arise from habit formation and from the acquisition of purposes and ideals. A child who has formed a strong habit of any kind tends to respond with that habitual reaction to the appropriate stimulation. This is one of the greatest values of habit in human behavior. The motivating force of habit is not unrelated to the simpler and more basic forms of motivation, however. To eat at a certain hour is a habit, and an individual becomes restless if his meal is delayed. To eat at some time, of course, is one of the most fundamental of motives, and the particular habit is based on this need. Thus the child may "learn" to like spinach and olives and may have a definite desire for them which he previously did not have. Many more complex forms of motivation shown in social situations have a similar origin. They are based on the original needs of the organism, but are developed through complicated processes of learning.
There is another very important factor in the relationship of habit to motivation. If a child has become accustomed or habituated to an excessive amount of some satisfaction he will be strongly motivated to seek it. The child who has been given candy cries for more. Similarly, the youngster who has been petted and protected in too great a degree is likely to spend the rest of his life looking for sympathy and guidance. To be dependent is satisfying for the child, but to have this satisfaction continued into later life is a social handicap.
Purposes and ideals also are motivating forces in the individual's behavior. A small boy may want a wagon, "skate-omobile," or scooter. He asks his father to get it for him, and the father does so. In this instance, little overt behavior is observable that may be attributed to the drive of his desire, want, or purpose. Suppose, however, that the father cannot afford to buy the scooter. The boy, if suitably trained to depend upon himself for the satisfaction of many of his own wants, may hunt about to find the necessary parts, materials, and tools and set to work making his own "skate-o-mobile" or wagon. For hours he may work at it, making many mistakes, bruising his fingers or getting splinters in them, having to try several times before he succeeds. Or the little girl who makes clothes for her doll has many things to learn and may have such high standards of excellence that she literally will work for hours, asking her mother many questions and doing things over and over, before she is satisfied with the result. Even at a younger age, long before children enter first grade, we see evidence of some purpose or, desire activating their behavior, as, for example, when a child of three or four years of age uses some blocks to build a house. The purpose in mind or incentive is not only a motivating force in the child's behavior, but it is also an organizing force through which his activities are integrated in accomplishing a given goal. The formation of suitable purposes and ideals is one of the most significant processes in the development of effective human personality. Reliance upon self in accomplishing many of his purposes is an excellent thing for the child. Even in infancy it seems desirable that the child relieve some of his own wants. If, for example, he is in an uncomfortable and cramped position and begins to cry, his own wriggling, squirming, and thrashing about are likely to overcome his discomfort. He thus learns to adjust independently, instead of expecting assistance. Purposes and ideals of children are likely to be concrete and relatively simple. They are often the expression or outgrowth of their "interests," which are thus also powerful motivating forces.
There is another very important factor in the relationship of habit to motivation. If a child has become accustomed or habituated to an excessive amount of some satisfaction he will be strongly motivated to seek it. The child who has been given candy cries for more. Similarly, the youngster who has been petted and protected in too great a degree is likely to spend the rest of his life looking for sympathy and guidance. To be dependent is satisfying for the child, but to have this satisfaction continued into later life is a social handicap.
Purposes and ideals also are motivating forces in the individual's behavior. A small boy may want a wagon, "skate-omobile," or scooter. He asks his father to get it for him, and the father does so. In this instance, little overt behavior is observable that may be attributed to the drive of his desire, want, or purpose. Suppose, however, that the father cannot afford to buy the scooter. The boy, if suitably trained to depend upon himself for the satisfaction of many of his own wants, may hunt about to find the necessary parts, materials, and tools and set to work making his own "skate-o-mobile" or wagon. For hours he may work at it, making many mistakes, bruising his fingers or getting splinters in them, having to try several times before he succeeds. Or the little girl who makes clothes for her doll has many things to learn and may have such high standards of excellence that she literally will work for hours, asking her mother many questions and doing things over and over, before she is satisfied with the result. Even at a younger age, long before children enter first grade, we see evidence of some purpose or, desire activating their behavior, as, for example, when a child of three or four years of age uses some blocks to build a house. The purpose in mind or incentive is not only a motivating force in the child's behavior, but it is also an organizing force through which his activities are integrated in accomplishing a given goal. The formation of suitable purposes and ideals is one of the most significant processes in the development of effective human personality. Reliance upon self in accomplishing many of his purposes is an excellent thing for the child. Even in infancy it seems desirable that the child relieve some of his own wants. If, for example, he is in an uncomfortable and cramped position and begins to cry, his own wriggling, squirming, and thrashing about are likely to overcome his discomfort. He thus learns to adjust independently, instead of expecting assistance. Purposes and ideals of children are likely to be concrete and relatively simple. They are often the expression or outgrowth of their "interests," which are thus also powerful motivating forces.
Social Motives
In addition to the motives that serve the individual's physiological needs, other forms of motivated behavior relate to his typical contacts with other people, which might be styled his social needs. These social motives were once thought to be primary and native (as by the "instinct theory") but may now be shown to arise from the simpler tissue needs and emotional states. Social motives are learned forms of behavior, and hence may differ considerably from person to person. In spite of individual differences, however, some patterns of social motivation are sufficiently common to justify enumerating them and indicating their principal sources.
(1) The need for prestige or the desire for social recognition is a very important social motive. To the stimulus of the presence of other people, the individual acts in such a way as to win attention, approval, and recognition. Much of the child's behavior is activated by this powerful motive. If deprived of the attention of a group, the child "shows off" or becomes noisy. Even serious delinquency may be motivated in this way, as when a youngster seeks to be a "tough guy" in the eyes of other children. On the other hand, some may find apparent modesty, docility, or humility a means of gaining recognition, as in the case of Uriah Heep who boasted of his "'umbleness."
The need for recognition and attention is derived from the satisfaction of the individual's physiological needs in infancy. Whenever ameliorative satisfactions such as those resulting from feeding, warming, or petting are administered, some person is present and is giving attention to the infant. Moreover, these services are frequently accompanied by kind words, regards, and gestures. Learning occurs, which causes the attention of human beings to be esteemed and sought throughout the rest of life.
(2) Another important social motive is the need for security. Persons, and especially children, need to feel that they are wanted and loved, and that they will be cared for. The origin of this motive is very similar to that of prestige and recognition. Because his needs are so great, the infant must depend on others for his welfare. Although constantly modified throughout the various stages of life, the security motive remains a strong one.
(3) The need for pre-eminence or mastery is very marked in child and adult behavior. Persons seek to excel, to get ahead, to worst rivals, and to overcome obstructions. If frustrated in the normal attainment of this goal, they often will assume an excessive aggressiveness toward substitute objects, resulting in bullying, quarrelsomeness, and, in some instances, delinquency.
The pre-eminence motive seems to be based on the rage behavior of infancy. If blocked or restrained in activity, the infant will display an intense emotional reaction and strong uncoordinated activity. Later, other situations come to arouse the same intensely motivated response, as when commands, the competition of other children, or material obstructions to be overcome, restrain him. The motivation, under proper training, is redirected from useless responses into persistence and effort. The pre-eminence desire is a very useful one in human, affairs, motivating desirable forms of ambition and labor as well as the less socialized efforts toward mastery.
(4) Persons are usually strongly motivated toward conformity. They desire to do the expected thing, to have the appearance of other people; they fear to be "different" or to receive scorn or blame. In a sense, this is the converse of the prestige motive but is not merely a passive desire to avoid losing approval. The conformity motive is undoubtedly related to the fear reactions of the infancy period. Whenever an adequate stimulus for fear, such as painful punishment by parents or a pummeling by child associates, is accompanied by blame, criticism, or condemnation, a conditioning occurs. Thereafter, attitudes of expressed or implied criticism tend to arouse the original strong, fear-motivated avoidance reactions. In general, conformity motivation is an inferior form of drive, which might well be eliminated. Social control is as adequately and more humanely achieved through the milder motives of prestige, security, and pre-eminence.
(1) The need for prestige or the desire for social recognition is a very important social motive. To the stimulus of the presence of other people, the individual acts in such a way as to win attention, approval, and recognition. Much of the child's behavior is activated by this powerful motive. If deprived of the attention of a group, the child "shows off" or becomes noisy. Even serious delinquency may be motivated in this way, as when a youngster seeks to be a "tough guy" in the eyes of other children. On the other hand, some may find apparent modesty, docility, or humility a means of gaining recognition, as in the case of Uriah Heep who boasted of his "'umbleness."
The need for recognition and attention is derived from the satisfaction of the individual's physiological needs in infancy. Whenever ameliorative satisfactions such as those resulting from feeding, warming, or petting are administered, some person is present and is giving attention to the infant. Moreover, these services are frequently accompanied by kind words, regards, and gestures. Learning occurs, which causes the attention of human beings to be esteemed and sought throughout the rest of life.
(2) Another important social motive is the need for security. Persons, and especially children, need to feel that they are wanted and loved, and that they will be cared for. The origin of this motive is very similar to that of prestige and recognition. Because his needs are so great, the infant must depend on others for his welfare. Although constantly modified throughout the various stages of life, the security motive remains a strong one.
(3) The need for pre-eminence or mastery is very marked in child and adult behavior. Persons seek to excel, to get ahead, to worst rivals, and to overcome obstructions. If frustrated in the normal attainment of this goal, they often will assume an excessive aggressiveness toward substitute objects, resulting in bullying, quarrelsomeness, and, in some instances, delinquency.
The pre-eminence motive seems to be based on the rage behavior of infancy. If blocked or restrained in activity, the infant will display an intense emotional reaction and strong uncoordinated activity. Later, other situations come to arouse the same intensely motivated response, as when commands, the competition of other children, or material obstructions to be overcome, restrain him. The motivation, under proper training, is redirected from useless responses into persistence and effort. The pre-eminence desire is a very useful one in human, affairs, motivating desirable forms of ambition and labor as well as the less socialized efforts toward mastery.
(4) Persons are usually strongly motivated toward conformity. They desire to do the expected thing, to have the appearance of other people; they fear to be "different" or to receive scorn or blame. In a sense, this is the converse of the prestige motive but is not merely a passive desire to avoid losing approval. The conformity motive is undoubtedly related to the fear reactions of the infancy period. Whenever an adequate stimulus for fear, such as painful punishment by parents or a pummeling by child associates, is accompanied by blame, criticism, or condemnation, a conditioning occurs. Thereafter, attitudes of expressed or implied criticism tend to arouse the original strong, fear-motivated avoidance reactions. In general, conformity motivation is an inferior form of drive, which might well be eliminated. Social control is as adequately and more humanely achieved through the milder motives of prestige, security, and pre-eminence.
Native and Acquired Factors in Motivation
Just as native or unlearned responses lie at the basis of all behavior, so the fundamental organic drives are the foundations of all motivation. The essential vigor of human responses arises from the internal conditions of the body. The elementary motives that have been discussed so far may be considered as native ones. Most of these, such as hunger, thirst, unfavorable temperature liberation through the skin, rest and sleep, elimination of waste products, certain aspects of sex, and the effects of emotional states, are internal. Some external stimuli also may be regarded as native arousers of behavior. These include tissue injury and other forms of excessively intense stimulation, and those milder skin stimuli leading to the so-called "love" responses. In general, the internal stimuli are originally more important than the external ones. External stimuli may set off responses, but these are directed, facilitated, or inhibited by the inner state. The total organism, with its characteristic structures and functions as organized into a living whole, possesses the energy and the modes of response which the stimulus, only releases. The key to man and to subhuman forms is to be sought more in the enormously complex energy changes going on within him than in the fortuitous play of outside energies working on him.
In the course of the development of motives, external stimuli come to play a larger part, but the essential controlling forces remain those within the organism.
The Modification of Motives
Problems of child behavior are complicated by the inextricable blending of native and acquired elements. Conditioning, learning, and habit formation begin the transformation of native responses immediately after birth. Acquired motives are largely developments from the early native ones, but the origin and development of a motive activating the child at the age of ten or twelve years only rarely can be traced in adequate detail. Habits, purposes, and ideals are still more complex forms of acquired motives, although even in these, the native elements might be found to furnish important parts of the total pattern, if we could only resolve it into its native and acquired components.
We see this process of modifying or conditioning drives in many features of child development, as when some external stimuli are substituted for the earlier internal native ones. Thus, at first the stimuli to play probably come from within, but later external stimulation may set off these activities, as when the child sees other children with whom he plays. The sight or smell of food may come to elicit responses which are aroused originally only by the actual pangs of hunger. Merely thinking about food may start off the flow of saliva which originally was activated, by the sight or smell of food. Thus, organic drives eventuating in positive (or negative) responses may become conditioned to various external stimuli. The sight, taste, smell, color, or merely the idea of an object associated with some unpleasant event may come to arouse the response originally evoked by that event. A child at a very early age is bitten by a large black dog. For years he may be decidedly afraid of dogs, and he may even find himself making incipient negative responses to a wide variety of objects that in some way resemble the black dog. A boy of six stepped on the tail of a sleeping Scotch collie, whereupon the dog lunged for the boy's throat, but jumped too high, sinking his two tusks in the boy's upper lip. For years the boy had a violent fear of large dogs, although he had always played with dogs and continued to play with dogs which were not strange to him. A boy of ten, trying to slide on the ice on a little pond into which refuse from a paper mill was dumped, broke through the thin ice which covered the shallow water and sank in above, his waist. For some minutes he was doubtful of his ability to extricate himself. Finally he got hold of a branch of a small willow tree and pulled himself toward the bank and out of the thick, slimy, vilesmelling, nauseating stuff. He, too, for years, at the sight of any place where the ground was yellowish, which had a small shallow puddle of clear water on part of it, and had a few small straggly willow trees about, not only felt afraid, but also felt strong disgust and some nausea at the anticipated thick, slimy, vile-smelling refuse. Even now, in maturity, although he cannot recall vividly the appearance of the place where he had the unpleasant experience, he occasionally sees a place which he instantly recognizes as like that of the childhood episode, and has some feeling of disgust and aversion.
It is evident from the above instances that the principal mechanism operating in the substitution of motive-stimuli is that of the conditioned reaction. By the simultaneous occurrence of an external stimulus with the original internal or sufficient one, the former becomes capable of evoking the behavior in question. This pattern of learning applies as clearly in the case of motives, likes, aversions, and interests as in simpler muscular or glandular responses.
Another class of stimuli, words, come to act as motives through the operation of the same processes of learning. The development of language permits the visual or auditory symbols of things to function in place of the things themselves. Commands, offers of reward, soothing commendations, all commonly act as motives at the earliest ages in which language is understood. As the child grows older, the motivating power of language symbols increases with his experience with them.
In the course of the development of motives, external stimuli come to play a larger part, but the essential controlling forces remain those within the organism.
The Modification of Motives
Problems of child behavior are complicated by the inextricable blending of native and acquired elements. Conditioning, learning, and habit formation begin the transformation of native responses immediately after birth. Acquired motives are largely developments from the early native ones, but the origin and development of a motive activating the child at the age of ten or twelve years only rarely can be traced in adequate detail. Habits, purposes, and ideals are still more complex forms of acquired motives, although even in these, the native elements might be found to furnish important parts of the total pattern, if we could only resolve it into its native and acquired components.
We see this process of modifying or conditioning drives in many features of child development, as when some external stimuli are substituted for the earlier internal native ones. Thus, at first the stimuli to play probably come from within, but later external stimulation may set off these activities, as when the child sees other children with whom he plays. The sight or smell of food may come to elicit responses which are aroused originally only by the actual pangs of hunger. Merely thinking about food may start off the flow of saliva which originally was activated, by the sight or smell of food. Thus, organic drives eventuating in positive (or negative) responses may become conditioned to various external stimuli. The sight, taste, smell, color, or merely the idea of an object associated with some unpleasant event may come to arouse the response originally evoked by that event. A child at a very early age is bitten by a large black dog. For years he may be decidedly afraid of dogs, and he may even find himself making incipient negative responses to a wide variety of objects that in some way resemble the black dog. A boy of six stepped on the tail of a sleeping Scotch collie, whereupon the dog lunged for the boy's throat, but jumped too high, sinking his two tusks in the boy's upper lip. For years the boy had a violent fear of large dogs, although he had always played with dogs and continued to play with dogs which were not strange to him. A boy of ten, trying to slide on the ice on a little pond into which refuse from a paper mill was dumped, broke through the thin ice which covered the shallow water and sank in above, his waist. For some minutes he was doubtful of his ability to extricate himself. Finally he got hold of a branch of a small willow tree and pulled himself toward the bank and out of the thick, slimy, vilesmelling, nauseating stuff. He, too, for years, at the sight of any place where the ground was yellowish, which had a small shallow puddle of clear water on part of it, and had a few small straggly willow trees about, not only felt afraid, but also felt strong disgust and some nausea at the anticipated thick, slimy, vile-smelling refuse. Even now, in maturity, although he cannot recall vividly the appearance of the place where he had the unpleasant experience, he occasionally sees a place which he instantly recognizes as like that of the childhood episode, and has some feeling of disgust and aversion.
It is evident from the above instances that the principal mechanism operating in the substitution of motive-stimuli is that of the conditioned reaction. By the simultaneous occurrence of an external stimulus with the original internal or sufficient one, the former becomes capable of evoking the behavior in question. This pattern of learning applies as clearly in the case of motives, likes, aversions, and interests as in simpler muscular or glandular responses.
Another class of stimuli, words, come to act as motives through the operation of the same processes of learning. The development of language permits the visual or auditory symbols of things to function in place of the things themselves. Commands, offers of reward, soothing commendations, all commonly act as motives at the earliest ages in which language is understood. As the child grows older, the motivating power of language symbols increases with his experience with them.
Other Physiological Conditions as Sources of Drives
When the skin is injured, strong defensive reactions follow, involving the skeletal muscles. If the pain is intense and continues for some time, the smooth musculature also is involved. Gently stroking or patting the skin tends toward relaxation of the muscles. Its therapeutic value in cases of restlessness, nervousness, and insomnia is well known and need not be based upon the psychoanalyst's view of stimulating "erotic zones."
Change or shifting of attention seems also to be a normal human activity, motivated by the boredom which follows a period of attentive regard (which may be too short for fatigue to enter) or by the urge to active seeking of different perceptual or other fields. Whatever the exact nature of this motive may be, we do not doubt its existence. Such a motive or drive is of inestimable value, insuring a wealth of sensory, perceptual, and other experiences.
Emotion as a Source of Motive
Emotional states constitute another important original source of vigorous and directed, or motivated, behavior. In the two preceding chapters, attention was called frequently to the intense character of the emotional response. An emotional state involves an upset condition of the visceral organs, which, in a sense, is not unlike the conditions found in hunger and the other appetitive drives. This visceral state may act as a strong internal stimulus, impelling the individual to activity.
Strong emotional states of the type of fear and rage are likely to stimulate intense physical activities which are, originally, of an uncoordinated nature. A three-year-old who is angered by another child's appropriating a cherished toy may resort to tears, may hold on to the toy, may try to pull it from the other's hands, or may strike, kick, or shove the offender. He selects one response or another according to the circumstances and his own past experiences, but the emotional state is the motivating factor throughout. As children mature, the character of the outward response to emotion usually becomes modified. A young child who is angered may respond by striking. A few years later, when enraged, he may respond only by angry words and facial expression. As he comes into the teens and social pressure is exerting its influence more effectively, he may respond merely by angry looks. As an adult the individual may not change his expression, but may make a remark that does not reveal the inner turmoil that he feels. Even in this last case, however, the stimulating effect of the emotional state may be present, although held in check, and may lead to the highly pertinent reply.
The milder organic states, such as those elicited by a full stomach, by loving attention, or by certain features of enjoying music or art, are sometimes designated as pleasant or relaxed emotions. These also may have an effect on the motivated behavior of the individual, reducing the activity of skeletal muscles and tending toward repose and compliance. Various internal states, therefore, may have the same effects as tissue needs in stimulating the various reactive mechanisms of the individual. The internal drives based on emotion are of great importance in the development of the social motives and in the mental, hygiene of the individual.
Change or shifting of attention seems also to be a normal human activity, motivated by the boredom which follows a period of attentive regard (which may be too short for fatigue to enter) or by the urge to active seeking of different perceptual or other fields. Whatever the exact nature of this motive may be, we do not doubt its existence. Such a motive or drive is of inestimable value, insuring a wealth of sensory, perceptual, and other experiences.
Emotion as a Source of Motive
Emotional states constitute another important original source of vigorous and directed, or motivated, behavior. In the two preceding chapters, attention was called frequently to the intense character of the emotional response. An emotional state involves an upset condition of the visceral organs, which, in a sense, is not unlike the conditions found in hunger and the other appetitive drives. This visceral state may act as a strong internal stimulus, impelling the individual to activity.
Strong emotional states of the type of fear and rage are likely to stimulate intense physical activities which are, originally, of an uncoordinated nature. A three-year-old who is angered by another child's appropriating a cherished toy may resort to tears, may hold on to the toy, may try to pull it from the other's hands, or may strike, kick, or shove the offender. He selects one response or another according to the circumstances and his own past experiences, but the emotional state is the motivating factor throughout. As children mature, the character of the outward response to emotion usually becomes modified. A young child who is angered may respond by striking. A few years later, when enraged, he may respond only by angry words and facial expression. As he comes into the teens and social pressure is exerting its influence more effectively, he may respond merely by angry looks. As an adult the individual may not change his expression, but may make a remark that does not reveal the inner turmoil that he feels. Even in this last case, however, the stimulating effect of the emotional state may be present, although held in check, and may lead to the highly pertinent reply.
The milder organic states, such as those elicited by a full stomach, by loving attention, or by certain features of enjoying music or art, are sometimes designated as pleasant or relaxed emotions. These also may have an effect on the motivated behavior of the individual, reducing the activity of skeletal muscles and tending toward repose and compliance. Various internal states, therefore, may have the same effects as tissue needs in stimulating the various reactive mechanisms of the individual. The internal drives based on emotion are of great importance in the development of the social motives and in the mental, hygiene of the individual.
Temperature through the skin, Rest and sleep
The human organism tends to maintain a constant body temperature at around 98.6° F. Regardless of weather or season the skin keeps the bodily temperature very nearly constant. Even a variation from normal of a few degrees is a sign of sickness, and a deviation of as much as eight degrees from the usual standard is evidence of very serious illness indeed.
The combustion processes of the body produce or liberate a great amount of heat. The metabolic functions of the body require only a small part of it. The remainder is given off, chiefly through the skin. With variations in the temperature surrounding the body, in the amount of clothing, and in internal bodily conditions (as in fever), marked changes occur in the rate of temperature release through the skin. An excessive rate of release or a subnormal rate is a powerful stimulus to activity. Many writers have emphasized the rôle of temperature and humidity upon man's mental and bodily efficiency and cultural development. They have shown that to torrid and arctic regions have not developed a high state of civilization and culture, and that science, literature, and other forms of art have been developed chiefly in the more favorable temperature of the temperate zones.
Unfavorable temperature liberation through the skin as one of the tissue needs giving rise to fundamental drives to overt behavior, resembling in this respect the great drives from hunger, thirst, and elimination. He also points out the place of this drive in seeking and developing shelter and clothing, and suggests that "the gregarious form of life among some animals at least is undoubtedly an outgrowth of unfavorable skin conditions," and that "their original 'sociability' is a huddling together of individuals who have been restlessly moving about until the warmth of each other's bodies furnished enough heat to allow the organism's to come to, rest -- as is easily observed in the nestling together of very young animals."
Rest and sleep
When the striped or skeletal muscles are fatigued the individual seeks rest, and when they are rested he again seeks activity. Activity and rest thus alternate with each other in a rhythm analogous to that of hunger and eating. Rest is a normal need of the organism and may be required by other factors than muscular fatigue alone. The hygiene value of rest and sleep is well known. The alternation of activity and rest is best seen in the case of the heart. The brief rest period after each beat occupies approximately one-third of the time, so that the heart muscle has abundant rest, which enables it to do its work for all the years of life.
That maturation plays a part in rest and sleep is shown by the decreasing amount of sleep needed as the child passes through the stages of infancy, early, middle, and late childhood, adolescence, and maturity. Problems of social control relate to training the child to sleep at times that meet his own needs and fit in with the convenience of the other members of the household. To regard sleep as a pleasure, and not to use it as a punishment seems highly desirable.
Sex
One of the most powerful drives is that of sex. During infancy and childhood the drive is manifested largely in connection with stimulating the erogenous zones and autoeroticism. The child's natural curiosity about sex is stimulated by many conditions and events in the environment. Inhibitions and taboos often repel the child's innocent and perfectly natural questions on sex matters as something nasty, unclean, or "bad," and prevent him from receiving adequate training. Accordingly, we reasonably may expect difficulties in the individual's control of this powerful fundamental drive along socially approved lines.
The combustion processes of the body produce or liberate a great amount of heat. The metabolic functions of the body require only a small part of it. The remainder is given off, chiefly through the skin. With variations in the temperature surrounding the body, in the amount of clothing, and in internal bodily conditions (as in fever), marked changes occur in the rate of temperature release through the skin. An excessive rate of release or a subnormal rate is a powerful stimulus to activity. Many writers have emphasized the rôle of temperature and humidity upon man's mental and bodily efficiency and cultural development. They have shown that to torrid and arctic regions have not developed a high state of civilization and culture, and that science, literature, and other forms of art have been developed chiefly in the more favorable temperature of the temperate zones.
Unfavorable temperature liberation through the skin as one of the tissue needs giving rise to fundamental drives to overt behavior, resembling in this respect the great drives from hunger, thirst, and elimination. He also points out the place of this drive in seeking and developing shelter and clothing, and suggests that "the gregarious form of life among some animals at least is undoubtedly an outgrowth of unfavorable skin conditions," and that "their original 'sociability' is a huddling together of individuals who have been restlessly moving about until the warmth of each other's bodies furnished enough heat to allow the organism's to come to, rest -- as is easily observed in the nestling together of very young animals."
Rest and sleep
When the striped or skeletal muscles are fatigued the individual seeks rest, and when they are rested he again seeks activity. Activity and rest thus alternate with each other in a rhythm analogous to that of hunger and eating. Rest is a normal need of the organism and may be required by other factors than muscular fatigue alone. The hygiene value of rest and sleep is well known. The alternation of activity and rest is best seen in the case of the heart. The brief rest period after each beat occupies approximately one-third of the time, so that the heart muscle has abundant rest, which enables it to do its work for all the years of life.
That maturation plays a part in rest and sleep is shown by the decreasing amount of sleep needed as the child passes through the stages of infancy, early, middle, and late childhood, adolescence, and maturity. Problems of social control relate to training the child to sleep at times that meet his own needs and fit in with the convenience of the other members of the household. To regard sleep as a pleasure, and not to use it as a punishment seems highly desirable.
Sex
One of the most powerful drives is that of sex. During infancy and childhood the drive is manifested largely in connection with stimulating the erogenous zones and autoeroticism. The child's natural curiosity about sex is stimulated by many conditions and events in the environment. Inhibitions and taboos often repel the child's innocent and perfectly natural questions on sex matters as something nasty, unclean, or "bad," and prevent him from receiving adequate training. Accordingly, we reasonably may expect difficulties in the individual's control of this powerful fundamental drive along socially approved lines.
Thirst, Elimination Sources of Simpler Motives
Thirst
Drives to overt behavior arise also from dryness of the mucous lining of the mouth and throat. Usually this means also a certain amount of water deficiency in the tissues. Saliva usually keeps the mouth and throat moist. As the body tissues become dehydrated, the saliva is no longer secreted in quantity sufficient to supply moisture to the mouth and throat.
As thirst develops the child or adult becomes restless, and, in fact, shows about the same rhythm phases as in hunger: restlessness, satisfaction, and quiescence. The significance and strength of the drive resulting from this tissue need are similar also to those in the case of hunger. The mechanisms involved are ready to function at birth.
Elimination
Many diverse structures and functional processes are involved in the elimination of waste products from the body. Water is eliminated by the lungs, the kidneys, the skin, and the lower intestine. Carbon dioxide is eliminated by the lungs, soluble salts by the kidneys, salts in solution by the skin, and insoluble waste products by the lower intestine. Of psychological importance are the features of these processes which are subject to modification and control for desirable social development. Breathing and the elimination of waste products by the sweat glands of the skin are well established soon after birth and are little modified by child training except in so far as training in breathing is given for singing, sports, and the like. The eliminative functions involving the bladder and lower bowel are of significance in child training because of their bearing on social adjustments. Adequate control of these processes is necessary for the protection of society, that is, for reasons of sanitation. Their control has significance also because of the social taboos developed about them, such as shame and modesty.
Three phases are observed in the rhythms of bladder and lower bowel elimination, corresponding to those in hunger and thirst. First is the period of accumulating pressure which directly necessitates and stimulates elimination. It is followed by that in which some response is made satisfying the drive. Finally ensues the period of relaxation, rest, or quiescence so far as elimination is concerned. Apparently, sensory experiences are involved, both in the increasing pressure of distention and in the eliminative responses, because voluntary control otherwise would be impossible.
During the first few months of post-natal life these processes are involuntary, but with maturation comes the possibility of developing voluntary control. With increasing age the frequency of these two eliminative responses decreases. The eighth month is usually the time to begin training in voluntary bladder control, and by the age of two years the child normally will be able to keep himself dry in the daytime. Similar control while asleep is not developed so soon, but if training is begun shortly after the end of the first year, control may be expected normally to develop by the end of the third year. Training in voluntary bowel control usually may begin advantageously about the end of the first month, and regular habits may be expected to be established by the end of the third or fourth month. The value of shame as an incentive in developing adequate voluntary control is seriously questioned. Intestinal or digestive difficulties, of course, may be expected to interfere with the regular routine being established for these functions.
Drives to overt behavior arise also from dryness of the mucous lining of the mouth and throat. Usually this means also a certain amount of water deficiency in the tissues. Saliva usually keeps the mouth and throat moist. As the body tissues become dehydrated, the saliva is no longer secreted in quantity sufficient to supply moisture to the mouth and throat.
As thirst develops the child or adult becomes restless, and, in fact, shows about the same rhythm phases as in hunger: restlessness, satisfaction, and quiescence. The significance and strength of the drive resulting from this tissue need are similar also to those in the case of hunger. The mechanisms involved are ready to function at birth.
Elimination
Many diverse structures and functional processes are involved in the elimination of waste products from the body. Water is eliminated by the lungs, the kidneys, the skin, and the lower intestine. Carbon dioxide is eliminated by the lungs, soluble salts by the kidneys, salts in solution by the skin, and insoluble waste products by the lower intestine. Of psychological importance are the features of these processes which are subject to modification and control for desirable social development. Breathing and the elimination of waste products by the sweat glands of the skin are well established soon after birth and are little modified by child training except in so far as training in breathing is given for singing, sports, and the like. The eliminative functions involving the bladder and lower bowel are of significance in child training because of their bearing on social adjustments. Adequate control of these processes is necessary for the protection of society, that is, for reasons of sanitation. Their control has significance also because of the social taboos developed about them, such as shame and modesty.
Three phases are observed in the rhythms of bladder and lower bowel elimination, corresponding to those in hunger and thirst. First is the period of accumulating pressure which directly necessitates and stimulates elimination. It is followed by that in which some response is made satisfying the drive. Finally ensues the period of relaxation, rest, or quiescence so far as elimination is concerned. Apparently, sensory experiences are involved, both in the increasing pressure of distention and in the eliminative responses, because voluntary control otherwise would be impossible.
During the first few months of post-natal life these processes are involuntary, but with maturation comes the possibility of developing voluntary control. With increasing age the frequency of these two eliminative responses decreases. The eighth month is usually the time to begin training in voluntary bladder control, and by the age of two years the child normally will be able to keep himself dry in the daytime. Similar control while asleep is not developed so soon, but if training is begun shortly after the end of the first year, control may be expected normally to develop by the end of the third year. Training in voluntary bowel control usually may begin advantageously about the end of the first month, and regular habits may be expected to be established by the end of the third or fourth month. The value of shame as an incentive in developing adequate voluntary control is seriously questioned. Intestinal or digestive difficulties, of course, may be expected to interfere with the regular routine being established for these functions.
Hunger: Physiological Conditions as Sources of Simpler Motives
The simpler types of motivation are based on the fundamental physiological processes of the organism. Although often overlooked or undervalued, these factors are of great importance in human life, and especially so in childhood. Much of the restless activity of the young is motivated by these simple drives, and even some more complex forms of motivation are learned elaborations of them. Among the physiological motives described here are hunger, thirst, elimination, temperature control, rest and sleep, and sex.
Hunger
Hunger is caused by contractions of the smooth muscles of the walls of the stomach, which seem to appear and disappear at regular intervals. That they provide a fundamental drive is well known. The hungry person is restless; the hungry infant likewise is restless and given to much overt activity which tends to subside as hunger is satisfied.
The importance of this drive in human history can hardly be overestimated. Food supply, with "fat" and "lean" years, is a fundamental problem in any national economy. In one primitive group fish was very scarce. Stealing fish was punishable by death, although stealing various other things such as another person's wife was not a capital offense. The hunger drive is equally important in the life of the child, with its implications for overt behavior and general bodily vigor.
The whole mechanism for the intake and digestion of food is ready to function at birth. With growth and maturation come changes, as well as through social control. Sometime around the sixth month the teeth begin to erupt, and when this process has proceeded far enough solid foods are included in the diet. Three phases of the hunger rhythm are found from birth. The period of restlessness, already referred to, is evidence of an organic need. Among infants this may be marked also by crying or other evidences of discomfort. This is followed by the responses of feeding -- sucking and swallowing. Then follows the period of quiescence during which the infant sleeps or is active in some way not related to hunger. In children and adults these three phases also are found. The feeding schedule and other features incident to the satisfaction of hunger (use of spoon, cup, etc.) are arranged not only to meet the child's requirements but also to meet those of society. As children develop, problems of poor adjustment may arise over eating, such as eating between meals, poor or irregular appetite, dislike for or refusal to eat certain foods, refusal of any food, refusal to drink from a cup or to feed self, etc. Lack of regular routine probably is responsible more than anything else for wanting to eat between meals and for poor or irregular appetite. On the whole, maladjustments like these seem to be due primarily to poor training; the child has learned the particular undesirable behavior from the training he has had.
Hunger
Hunger is caused by contractions of the smooth muscles of the walls of the stomach, which seem to appear and disappear at regular intervals. That they provide a fundamental drive is well known. The hungry person is restless; the hungry infant likewise is restless and given to much overt activity which tends to subside as hunger is satisfied.
The importance of this drive in human history can hardly be overestimated. Food supply, with "fat" and "lean" years, is a fundamental problem in any national economy. In one primitive group fish was very scarce. Stealing fish was punishable by death, although stealing various other things such as another person's wife was not a capital offense. The hunger drive is equally important in the life of the child, with its implications for overt behavior and general bodily vigor.
The whole mechanism for the intake and digestion of food is ready to function at birth. With growth and maturation come changes, as well as through social control. Sometime around the sixth month the teeth begin to erupt, and when this process has proceeded far enough solid foods are included in the diet. Three phases of the hunger rhythm are found from birth. The period of restlessness, already referred to, is evidence of an organic need. Among infants this may be marked also by crying or other evidences of discomfort. This is followed by the responses of feeding -- sucking and swallowing. Then follows the period of quiescence during which the infant sleeps or is active in some way not related to hunger. In children and adults these three phases also are found. The feeding schedule and other features incident to the satisfaction of hunger (use of spoon, cup, etc.) are arranged not only to meet the child's requirements but also to meet those of society. As children develop, problems of poor adjustment may arise over eating, such as eating between meals, poor or irregular appetite, dislike for or refusal to eat certain foods, refusal of any food, refusal to drink from a cup or to feed self, etc. Lack of regular routine probably is responsible more than anything else for wanting to eat between meals and for poor or irregular appetite. On the whole, maladjustments like these seem to be due primarily to poor training; the child has learned the particular undesirable behavior from the training he has had.
What are the fundamental drives in children?
What are the fundamental drives in children? What are the important motives directing their conduct? How are these developed or modified? Whence do motives come, or what are their sources? What is the relative importance of original nature and learning in motivation? What part do purposes, attitudes, ideals, and interests play in motivating childhood behavior? In what things are children interested at various ages from birth to maturity? These are important problems to which we must now turn our attention if we would secure a fruitful understanding of child nature.
Teachers, parents, and others who guide and direct the behavior of children can do so to best advantage, only if they really understand them. Obviously, such an understanding is dependent upon knowing why the child at a particular time does what he does.
A nine-year-old girl, large for her age, comes home with her best shoes not only covered with mud, but her stockings or socks are also covered with mud halfway to her knees, and splotches of mud are on her dress. The mother has told her "a thousand times" to keep out of the mud and has scolded and punished her for getting her shoes and other clothes muddy. To her the girl's behavior is perverse indeed, and the child may be punished severely for disobeying her mother's previous ultimatum, especially if the mother is crowded with work, has a headache, or is under some other strain. A boy of eight, going to school, takes a short-cut across the corner of a large newly seeded lawn, although he has been told repeatedly to keep out. He is a quiet, well-behaved boy, but persists in cutting across the lawn despite scoldings and threats to notify his parents and the police. Regardless of what is done to handle these two cases, the mother and the lawnowner probably can secure a more effective modification of behavior if they understand why the girl got so muddy and why the boy uses the much objected-to short-cut. The girl, taunted and teased by a young bully's remarks, finally in desperation gives chase through a muddy garden and settles the matter. While on his way to school when in the first grade the boy had been very badly frightened by a cross dog on the next street. He had cut through a vacant lot, and for two years had been going to school this way. A new house had been built and the lot graded and seeded. The boy was still using the accustomed way although the cross dog no longer lived on the next street.
Rational guidance and control of children are contingent upon understanding the motives which activate them.
Some of the earlier attempts at understanding human behavior postulated a series of entities known as instincts which acted as drives, or springs to action. Thus, an individual was said to have a drive or urge to do those things which led to selfpreservation because he had an instinct or instinctive urge of selfpreservation. He was said to want to be with other persons because of the drive from the gregarious or social instinct. If he tore things to pieces this was because of his instinct of destructiveness, or if he put things together in some way it was because of the constructive instinct! On the whole such attempts to understand human motives have not carried us very far. Part of the diffculty, but not all, lies in the fact that the term instinct has been used with at least two diverse meanings. Sometimes it means stimulus arousal of an activity, and sometimes it means a pattern or kind of activity itself. Thus it is used to mean the motivation of an activity, as in pugnacity, curiosity, gregariousnes, parental love, and the like; whereas in other cases it refers to the kind of activity, as when it was alleged that walking, manipulation, collecting, etc., were instincts.
Trying to understand complex human behavior by postulating such entities seems to break down in the study of actual cases. The discussion of mass activity in several previous chapters should make it clear that definite, clear-cut, specific, fixed-inadvance patterns of behavior are rare indeed, and that diffuse, non-specific mass activity is generally the rule, the former developing after experience, learning, or-habit formation has played its part in the infant's development. The definite patterns of response called for by the instinct theory are not found upon careful observation of infants during the first few days or weeks of post-natal life; neither does it seem fruitful to suppose entities (instincts or springs of action) concealed inside us, which, when stimulated, make us do this, that, or some other thing. Such a description of human motivation has little to commend it aside from tradition.
Teachers, parents, and others who guide and direct the behavior of children can do so to best advantage, only if they really understand them. Obviously, such an understanding is dependent upon knowing why the child at a particular time does what he does.
A nine-year-old girl, large for her age, comes home with her best shoes not only covered with mud, but her stockings or socks are also covered with mud halfway to her knees, and splotches of mud are on her dress. The mother has told her "a thousand times" to keep out of the mud and has scolded and punished her for getting her shoes and other clothes muddy. To her the girl's behavior is perverse indeed, and the child may be punished severely for disobeying her mother's previous ultimatum, especially if the mother is crowded with work, has a headache, or is under some other strain. A boy of eight, going to school, takes a short-cut across the corner of a large newly seeded lawn, although he has been told repeatedly to keep out. He is a quiet, well-behaved boy, but persists in cutting across the lawn despite scoldings and threats to notify his parents and the police. Regardless of what is done to handle these two cases, the mother and the lawnowner probably can secure a more effective modification of behavior if they understand why the girl got so muddy and why the boy uses the much objected-to short-cut. The girl, taunted and teased by a young bully's remarks, finally in desperation gives chase through a muddy garden and settles the matter. While on his way to school when in the first grade the boy had been very badly frightened by a cross dog on the next street. He had cut through a vacant lot, and for two years had been going to school this way. A new house had been built and the lot graded and seeded. The boy was still using the accustomed way although the cross dog no longer lived on the next street.
Rational guidance and control of children are contingent upon understanding the motives which activate them.
Some of the earlier attempts at understanding human behavior postulated a series of entities known as instincts which acted as drives, or springs to action. Thus, an individual was said to have a drive or urge to do those things which led to selfpreservation because he had an instinct or instinctive urge of selfpreservation. He was said to want to be with other persons because of the drive from the gregarious or social instinct. If he tore things to pieces this was because of his instinct of destructiveness, or if he put things together in some way it was because of the constructive instinct! On the whole such attempts to understand human motives have not carried us very far. Part of the diffculty, but not all, lies in the fact that the term instinct has been used with at least two diverse meanings. Sometimes it means stimulus arousal of an activity, and sometimes it means a pattern or kind of activity itself. Thus it is used to mean the motivation of an activity, as in pugnacity, curiosity, gregariousnes, parental love, and the like; whereas in other cases it refers to the kind of activity, as when it was alleged that walking, manipulation, collecting, etc., were instincts.
Trying to understand complex human behavior by postulating such entities seems to break down in the study of actual cases. The discussion of mass activity in several previous chapters should make it clear that definite, clear-cut, specific, fixed-inadvance patterns of behavior are rare indeed, and that diffuse, non-specific mass activity is generally the rule, the former developing after experience, learning, or-habit formation has played its part in the infant's development. The definite patterns of response called for by the instinct theory are not found upon careful observation of infants during the first few days or weeks of post-natal life; neither does it seem fruitful to suppose entities (instincts or springs of action) concealed inside us, which, when stimulated, make us do this, that, or some other thing. Such a description of human motivation has little to commend it aside from tradition.
We require ten inorganic or mineral elements
Proteins consist of giant molecules which are resolved during digestion into about twenty relatively simple organic compounds known as amino-acids. We know that two of these can be synthesized by the body, and, pending further investigations, we may assume that the remaining eighteen must be supplied by the food. We must have the sugar glucose, which may be taken as such or derived from cane or milk sugar or from the various starches. These are all changed by the organs of digestion so as to introduce only glucose into the blood. We require at least ten inorganic or mineral elements: sodium, potassium, calcium, magnesium, chlorine, iodine, phosphorus, sulphur, iron, and copper. Probably this list of indispensable inorganic elements will eventually be extended to include several others, such as manganese, zinc, silicon, fluorine, and possibly nickel and cobalt, boron, etc. These last appear to be necessary for the development of plants, and may also be necessary for that of animals. At least six nutrient principles, called vitamins A, B, C, D, E, and G, are known to be required for normal nutrition. Among the twenty or more fatty acids known to chemists, at least twelve occur in the fats of our ordinary foods, but it appears from the results of experiment that only one of these, namely, linoleic acid, cannot be synthesized by the body from carbohydrate molecules. From the data available we may say with some assurance that the simplest diet which would furnish everything necessary for normal nutrition must contain appropriate proportions of at least thirty-six simple chemical substances. Actually, we eat daily many times this number in our ordinary foods of animal and vegetable origin.
Methods have been developed by means of which experiments on animals fed a single natural food (wheat, maize, etc.), which does not alone support satisfactory nutrition, supplemented with single or multiple additions of the indispensable nutrients, yield information concerning the nature of their deficiencies. Such experiments may be made nearly quantitative. Through such studies we have secured a considerable body of knowledge concerning the extent to which each of our more important natural foods-cereal grains, tubers, fruits, roots, leaves, meats, milk, eggs, etc.--furnishes the body with the indispensable nutrients. In addition, such experiments have shown us the nature and extent of the deficiencies of the different natural foods. On the basis of such data it is possible to theorize concerning which natural foods, individually lacking or deficient in one or another food principle, should, when combined, supplement each other's deficiencies. Experimental verification of predicted results confirms in a highly satisfactory manner the belief that we understand, to a great extent, the nutritive needs of the body and the dietary properties of most of our natural and manufactured foods.
Since most foods have been shown to be deficient or lacking in one or more of the nutrient principles, it is necessary for us to combine foods of unlike composition so that one will provide what the other lacks. Herein lies the cause of safety in variety in eating. The whole wheat kernel, which many people have long believed to be a complete food, is incapable, when fed as the sole source of nutriment, of supporting growth of the young or prolonged health in the adult. It is deficient in three respects: (1) it lacks sufficient calcium; (2) it lacks sufficient vitamin A; and (3) its proteins require supplementing with proteins from other sources which supply in abundance certain amino-acids which the wheat proteins contain in amounts too small to serve as building stones when food proteins are converted into body proteins. Even though wheat is supplemented with one or two of these substances in which it is deficient, the nutrition of an animal will not be so good as it will if all three are added to the diet.
Methods have been developed by means of which experiments on animals fed a single natural food (wheat, maize, etc.), which does not alone support satisfactory nutrition, supplemented with single or multiple additions of the indispensable nutrients, yield information concerning the nature of their deficiencies. Such experiments may be made nearly quantitative. Through such studies we have secured a considerable body of knowledge concerning the extent to which each of our more important natural foods-cereal grains, tubers, fruits, roots, leaves, meats, milk, eggs, etc.--furnishes the body with the indispensable nutrients. In addition, such experiments have shown us the nature and extent of the deficiencies of the different natural foods. On the basis of such data it is possible to theorize concerning which natural foods, individually lacking or deficient in one or another food principle, should, when combined, supplement each other's deficiencies. Experimental verification of predicted results confirms in a highly satisfactory manner the belief that we understand, to a great extent, the nutritive needs of the body and the dietary properties of most of our natural and manufactured foods.
Since most foods have been shown to be deficient or lacking in one or more of the nutrient principles, it is necessary for us to combine foods of unlike composition so that one will provide what the other lacks. Herein lies the cause of safety in variety in eating. The whole wheat kernel, which many people have long believed to be a complete food, is incapable, when fed as the sole source of nutriment, of supporting growth of the young or prolonged health in the adult. It is deficient in three respects: (1) it lacks sufficient calcium; (2) it lacks sufficient vitamin A; and (3) its proteins require supplementing with proteins from other sources which supply in abundance certain amino-acids which the wheat proteins contain in amounts too small to serve as building stones when food proteins are converted into body proteins. Even though wheat is supplemented with one or two of these substances in which it is deficient, the nutrition of an animal will not be so good as it will if all three are added to the diet.
Saturday, March 1, 2008
Forms of muscle irritability, contractility, conductivity, metabolic activity
All forms of muscle possess the following physiologic properties: irritability, contractility, conductivity, and metabolic activity. The specific function of muscle is to shorten for the purpose of movement, hence, its most specialized property is contractility. This property is most marked in skeletal muscle.
When a muscle responds, certain rather definite changes occur within it, namely, mechanical change, chemical change, thermal change, and the production of electricity and sound.
During contraction muscle changes its shape but its volume remains unchanged.
In response to a single stimulus, a muscle gives a single twitch, the record of which is known as a myogram. The myogram of a frog's muscle shows a latent period of 0.01 second, a contraction phase of 0.04 second, and a relaxation phase of 0.05 second. The various phases of the response of human muscles, although varying somewhat from those of the frog muscles, have about the same relative duration.
Following a series of repeated stimuli (two to five per second), the first few contractions progressively increase in extent to a maximum--treppe-after which the responses soon become less and less effective as fatigue develops. Fatigue prolongs each of the phases of the response--especially the relaxation phase. As the relaxation phase is lengthened the succeeding stimulus begins to reach the muscle before relaxation is completed. The new contraction begins at this point leaving a contraction remainder or contracture.When the stimuli are applied more rapidly the muscle may be held in a state of continuous contraction or complete tetanus. If a partial relaxation is permitted, the tetanus is now incomplete and is known as incomplete tetanus. The importance of tetanus lies in the fact that practically every voluntary and reflex response in man is of this nature. They possess three fundamentally important characteristics, namely, maintenance, fusion of separate contractions, and a summation of single responses.Although the mechanical response is continuous and maintained, it can be shown by the electrical change and sound produced that, within certain limits, the internal response is discontinuous. This discontinuous phase is, however, limited by an inherent period of forced rest imposed upon the muscle due to what is known as the refractory period.Within certain limits, a rise or fall of temperature increases or decreases respectively the rate of response. Again it is the relaxation phase which is especially affected. At a certain low temperature activity is reversibly suspended; at a certain high temperature it is irreversibly lost. These temperatures differ from animal to animal.The skeletal muscle fiber responds as a unit, that is, when stimulated it either gives a maximal contraction or fails to respond at all,--the "all-ornothing" phenomenon. Graded response is a function of the whole muscle, the strength of the response being determined by the number of fibers acting at any given time. Heart muscle in its entirety obeys the same law.
When a muscle responds, certain rather definite changes occur within it, namely, mechanical change, chemical change, thermal change, and the production of electricity and sound.
During contraction muscle changes its shape but its volume remains unchanged.
In response to a single stimulus, a muscle gives a single twitch, the record of which is known as a myogram. The myogram of a frog's muscle shows a latent period of 0.01 second, a contraction phase of 0.04 second, and a relaxation phase of 0.05 second. The various phases of the response of human muscles, although varying somewhat from those of the frog muscles, have about the same relative duration.
Following a series of repeated stimuli (two to five per second), the first few contractions progressively increase in extent to a maximum--treppe-after which the responses soon become less and less effective as fatigue develops. Fatigue prolongs each of the phases of the response--especially the relaxation phase. As the relaxation phase is lengthened the succeeding stimulus begins to reach the muscle before relaxation is completed. The new contraction begins at this point leaving a contraction remainder or contracture.When the stimuli are applied more rapidly the muscle may be held in a state of continuous contraction or complete tetanus. If a partial relaxation is permitted, the tetanus is now incomplete and is known as incomplete tetanus. The importance of tetanus lies in the fact that practically every voluntary and reflex response in man is of this nature. They possess three fundamentally important characteristics, namely, maintenance, fusion of separate contractions, and a summation of single responses.Although the mechanical response is continuous and maintained, it can be shown by the electrical change and sound produced that, within certain limits, the internal response is discontinuous. This discontinuous phase is, however, limited by an inherent period of forced rest imposed upon the muscle due to what is known as the refractory period.Within certain limits, a rise or fall of temperature increases or decreases respectively the rate of response. Again it is the relaxation phase which is especially affected. At a certain low temperature activity is reversibly suspended; at a certain high temperature it is irreversibly lost. These temperatures differ from animal to animal.The skeletal muscle fiber responds as a unit, that is, when stimulated it either gives a maximal contraction or fails to respond at all,--the "all-ornothing" phenomenon. Graded response is a function of the whole muscle, the strength of the response being determined by the number of fibers acting at any given time. Heart muscle in its entirety obeys the same law.
Discontinuous nature of tetanic contractions and refractory period
Although the mechanical response in complete tetanus is maintained and continuous, that is to say, no sign of relaxation is apparent, the true character of the response to the rapidly repeated stimuli can be shown to be discontinuous. The most striking proof of this fact is the electrical change. Within certain limits, the number of electrical changes corresponds with the rate of stimulation. A further proof of the discontinuous nature of tetanic contractions lies in the sounds produced by contracting muscles. This correspondence between the internal response of muscle and the rate of stimulation will extend from a single stimulus up to about one thousand stimuli per second for the muscles of man and other warmblooded animals. When the rate of stimuli exceeds this higher figure, the muscle fails to respond to each stimulus but responds only to every other one.
This result is due to the fact that immediately following a response to a single stimulus there is a period, as it were, of forced rest or period of adjustment during which the muscle is non-irritable and fails to respond. This brief period is known as the refractory period and is of about 0.005 second duration in skeletal muscle. It serves as a means of further protection to the muscle against a demand which is beyond its capacity. This discontinuous character of the response is to be explained on the basis of the discontinuous nature of the chemical changes occurring in response to the rapidly repeated stimuli. Likewise the refractory period and limits to which these separate changes can take place must find their explanation in the factors controlling the biochemical reactions involved. The refractory period of muscle is so brief, however, that it probably never functions to limit the frequency of the response in man.
The importance of tetanic contractions lies in the fact that this type of contraction is practically the only one to be found in the human body during muscular exercise or activity. This fact, in the intact human body, is due to the manner in which the muscles receive their stimuli and are controlled through the central nervous system. When a muscle or group of muscles is called into action, a shower of impulses is sent from the nerve centers over the motor nerve fibers which innervate these muscles. A few, many or all of the muscle fibers of the muscles involved may be stimulated, the response being graded in proportion.
This result is due to the fact that immediately following a response to a single stimulus there is a period, as it were, of forced rest or period of adjustment during which the muscle is non-irritable and fails to respond. This brief period is known as the refractory period and is of about 0.005 second duration in skeletal muscle. It serves as a means of further protection to the muscle against a demand which is beyond its capacity. This discontinuous character of the response is to be explained on the basis of the discontinuous nature of the chemical changes occurring in response to the rapidly repeated stimuli. Likewise the refractory period and limits to which these separate changes can take place must find their explanation in the factors controlling the biochemical reactions involved. The refractory period of muscle is so brief, however, that it probably never functions to limit the frequency of the response in man.
The importance of tetanic contractions lies in the fact that this type of contraction is practically the only one to be found in the human body during muscular exercise or activity. This fact, in the intact human body, is due to the manner in which the muscles receive their stimuli and are controlled through the central nervous system. When a muscle or group of muscles is called into action, a shower of impulses is sent from the nerve centers over the motor nerve fibers which innervate these muscles. A few, many or all of the muscle fibers of the muscles involved may be stimulated, the response being graded in proportion.
Compound or tetanic contractions of muscle
A second method of grading the response of a muscle as a whole is by altering the frequency at which the separate stimuli reach the muscle. When a frog's gastrocnemius muscle is stimulated with a series of rapidly repeated stimuli (twenty or more per second) it remains in a state of more or less maintained contraction as long as the stimuli are continued, or until fatigue develops to terminate the response. This maintained contraction is known as physiological tetanus. When the stimuli follow each other so rapidly as to prevent even partial relaxation, the response is termed complete tetanus. If, on the other hand, the stimuli are less frequent and permit the muscle to partly relax, but not completely, before the following stimulus initiates a new response and the myogram shows a condition of incomplete maintenance of the contractile phase, it is then known as incomplete tetanus. Various grades of incomplete tetanus are possible. Complete tetanus probably involves all of the muscle fibers of which a muscle is composed.
Tetanic contractions present three fundamentally important characteristic, namely: first, maintenance or increased duration over that of the simple twitch, second, the more or less fusion of the separate responses initiated within the muscle by the separate stimuli, and third, the phenomenon of summation of the single responses so that the extent of the contraction in tetanus is much greater than that presented by a simple twitch. It would seem that in a single twitch acting against a load, the contractile stress of the muscle passes off before the load is lifted to the maximum height possible. Summation is probably due to the added mechanical effect of the load since in the second response the lever stands at a higher abscissa. The single twitch is inefficient because it is too brief except for handling very light loads against very low resistances. This principle of summation was inferred in the discussion of fatigue given in a previous paragraph. It depends upon the application of a second stimulus at some time during the contraction or relaxation phase of the response initiated by a previous stimulus.
The greatest summation occurs when the second stimulus is so timed as to reach the muscle just as it reaches the state of greatest tension, and diminishes as it appears earlier or later in the contraction phase. Any conditions which will prolong the contraction and especially the relaxation phase, such as fatigue, diminished temperature, and others, will diminish the number of stimuli necessary to induce a state of tetanus and, therefore, will bring about an exaggeration of the normal response.
Tetanic contractions present three fundamentally important characteristic, namely: first, maintenance or increased duration over that of the simple twitch, second, the more or less fusion of the separate responses initiated within the muscle by the separate stimuli, and third, the phenomenon of summation of the single responses so that the extent of the contraction in tetanus is much greater than that presented by a simple twitch. It would seem that in a single twitch acting against a load, the contractile stress of the muscle passes off before the load is lifted to the maximum height possible. Summation is probably due to the added mechanical effect of the load since in the second response the lever stands at a higher abscissa. The single twitch is inefficient because it is too brief except for handling very light loads against very low resistances. This principle of summation was inferred in the discussion of fatigue given in a previous paragraph. It depends upon the application of a second stimulus at some time during the contraction or relaxation phase of the response initiated by a previous stimulus.
The greatest summation occurs when the second stimulus is so timed as to reach the muscle just as it reaches the state of greatest tension, and diminishes as it appears earlier or later in the contraction phase. Any conditions which will prolong the contraction and especially the relaxation phase, such as fatigue, diminished temperature, and others, will diminish the number of stimuli necessary to induce a state of tetanus and, therefore, will bring about an exaggeration of the normal response.
The unit of the nervous system is the neurone
The unit of the nervous system is the neurone,--a nerve cell with all of its processes. The nervous system is composed of myriads of neurones joined into a network by means of synapses.
Each muscle fiber is supplied by at least one motor nerve fiber which ends beneath the sarcolemma in the motor end organ. This constitutes the efferent nerve supply. From the muscle and tendon spindles, muscles make afferent connections with the brain and spinal cord (central nervous system), in part sensory and in part non-sensory.
The simple nervous connections between peripheral receptors to the center (afferent) and the return to the effector (efferent) is known as a reflex arc, and is composed of at least two neurones. More complex arcs are established by means of one or more connector neurones and may extend to the opposite side of the cord, to other levels, and to the cerebrum. In the last case they become sensory fibers since they arouse sensations. Voluntary discharges may issue from the motor area of the cerebrum to the lower reflex mechanisms and elicit voluntary movements.The term reflex action is used to designate involuntary action. Reflexes are dependent upon the integrity of the reflex arc. Pavlov has classified all known reflex actions into unconditioned or inborn reflexes, and conditioned or acquired reflexes.Muscle tonus is that state of partially maintained contraction of muscle by which its length and tension, especially true of antagonistic muscles, are automatically adapted to the new positions taken by parts of the body as in locomotion or of parts of the body to the whole as in posture.
The physical properties of muscle, extensibility and elasticity, are increased or decreased directly as muscle tonus is increased or decreased.Muscle tonus and postural tonus are dependent upon the integrity of the myotatic or monomuscular arc, and upon connections with the semicircular canals, cerebrum, and cerebellum. Loss of any one will alter muscle and postural tonus.The nicety of adjustment between the position of the body to its environment or of the parts of the body to the whole, of muscle tonus, action of antagonists, and in postural tonus is dependent upon the phenomena of reciprocal action and reciprocal innervation. When one group of muscles contract an antagonistic group must relax and vice versa. Movements of locomotion would be impossible without these mechanisms.
Each muscle fiber is supplied by at least one motor nerve fiber which ends beneath the sarcolemma in the motor end organ. This constitutes the efferent nerve supply. From the muscle and tendon spindles, muscles make afferent connections with the brain and spinal cord (central nervous system), in part sensory and in part non-sensory.
The simple nervous connections between peripheral receptors to the center (afferent) and the return to the effector (efferent) is known as a reflex arc, and is composed of at least two neurones. More complex arcs are established by means of one or more connector neurones and may extend to the opposite side of the cord, to other levels, and to the cerebrum. In the last case they become sensory fibers since they arouse sensations. Voluntary discharges may issue from the motor area of the cerebrum to the lower reflex mechanisms and elicit voluntary movements.The term reflex action is used to designate involuntary action. Reflexes are dependent upon the integrity of the reflex arc. Pavlov has classified all known reflex actions into unconditioned or inborn reflexes, and conditioned or acquired reflexes.Muscle tonus is that state of partially maintained contraction of muscle by which its length and tension, especially true of antagonistic muscles, are automatically adapted to the new positions taken by parts of the body as in locomotion or of parts of the body to the whole as in posture.
The physical properties of muscle, extensibility and elasticity, are increased or decreased directly as muscle tonus is increased or decreased.Muscle tonus and postural tonus are dependent upon the integrity of the myotatic or monomuscular arc, and upon connections with the semicircular canals, cerebrum, and cerebellum. Loss of any one will alter muscle and postural tonus.The nicety of adjustment between the position of the body to its environment or of the parts of the body to the whole, of muscle tonus, action of antagonists, and in postural tonus is dependent upon the phenomena of reciprocal action and reciprocal innervation. When one group of muscles contract an antagonistic group must relax and vice versa. Movements of locomotion would be impossible without these mechanisms.
Reciprocal action and reciprocal innervation of antagonistic muscles
In the foregoing survey of the mechanisms involved in muscular activity, it has been pointed out that both reflex and voluntary responses may become very complex yet are coördinated and may be purposeful and protective in character. Such responses cannot be mediated through a single muscle, but by a nicety of balance between the activities of groups of antagonistic muscles. This balance is the resultant of a reciprocal activity existing between muscles which act upon the levers of a certain joint or series of joints in opposite directions. When one group of muscles is stimulated, the other is thrown into a state of inhibition in order that the action may take place without opposition. Such a condition is found at all joints where flexion and extension, abduction and adduction, and rotation take place. Since this power of coördination does not reside in the muscles, but in the central nervous system, a reciprocal innervation of the opposing muscles in any particular instance is required.
The mode of innervation is such that when one group of similarly acting muscles, as the quadriceps in the extension of the leg, is stimulated, the antagonistic flexor group (hamstrings) is inhibited. When the reverse action occurs (flexion) the hamstrings are stimulated while the quadriceps are inhibited. That this actually occurs has been proved experimentally. The nervous mechanism necessary for such an allied or synergic response is known as reciprocal innervation. The flexors (hamstrings) are supplied by their monomuscular arcs from the fifth lumbar to the second sacral nerves. The two sets of arcs are connected by connector neurones within the cord and the number of nerve fibers involved probably amounts to several thousands. Impulses which arise in the voluntary centers of the cerebrum may act through this local mechanism. Similar relationships are to be observed at many other joints and in the muscles of the eyes.
Inhibitory nerves for skeletal muscles have never been demonstrated and it is generally believed that they do not exist. If this is the case the mechanism for reciprocal innervation must then be looked for in the central nervous system. Motor nerve cells in the spinal cord may be either stimulated or inhibited, that is, their activity may be augmented or diminished. Inhibition may be produced by diminishing or blocking the motor discharge issuing from the nerve centers over the efferent nerves and may affect a few or all of the nerve fibers involved. In any given reflex action, one and the same stimulus will increase the activity of the flexor center and simultaneously inhibit that of the extensor center. Conversely, when the stimulus is such as to excite the extensor center the activity of the flexor center is inhibited. Thus the influence on the two centers for antagonistic groups of muscles are of opposite sign.
Reciprocal innervation is not limited to the muscles of a single part, but may extend to other parts as, for example, when two or more parts are employed in progressive movements, such as walking. These mechanisms become more complex. From the same diagram, it may be seen that when the extensors of the supporting limb are excited and enter into contraction those of the opposite limb (progressing) must be inhibited, that is, their activity is of opposite sign. Exactly the opposite order of events is occurring in the flexors, namely, they are inhibited in the supporting and excited in the progressing limbs.
The mode of innervation is such that when one group of similarly acting muscles, as the quadriceps in the extension of the leg, is stimulated, the antagonistic flexor group (hamstrings) is inhibited. When the reverse action occurs (flexion) the hamstrings are stimulated while the quadriceps are inhibited. That this actually occurs has been proved experimentally. The nervous mechanism necessary for such an allied or synergic response is known as reciprocal innervation. The flexors (hamstrings) are supplied by their monomuscular arcs from the fifth lumbar to the second sacral nerves. The two sets of arcs are connected by connector neurones within the cord and the number of nerve fibers involved probably amounts to several thousands. Impulses which arise in the voluntary centers of the cerebrum may act through this local mechanism. Similar relationships are to be observed at many other joints and in the muscles of the eyes.
Inhibitory nerves for skeletal muscles have never been demonstrated and it is generally believed that they do not exist. If this is the case the mechanism for reciprocal innervation must then be looked for in the central nervous system. Motor nerve cells in the spinal cord may be either stimulated or inhibited, that is, their activity may be augmented or diminished. Inhibition may be produced by diminishing or blocking the motor discharge issuing from the nerve centers over the efferent nerves and may affect a few or all of the nerve fibers involved. In any given reflex action, one and the same stimulus will increase the activity of the flexor center and simultaneously inhibit that of the extensor center. Conversely, when the stimulus is such as to excite the extensor center the activity of the flexor center is inhibited. Thus the influence on the two centers for antagonistic groups of muscles are of opposite sign.
Reciprocal innervation is not limited to the muscles of a single part, but may extend to other parts as, for example, when two or more parts are employed in progressive movements, such as walking. These mechanisms become more complex. From the same diagram, it may be seen that when the extensors of the supporting limb are excited and enter into contraction those of the opposite limb (progressing) must be inhibited, that is, their activity is of opposite sign. Exactly the opposite order of events is occurring in the flexors, namely, they are inhibited in the supporting and excited in the progressing limbs.
Postural tonus
The most significant role of skeletal-muscle tonus as a factor in bodily activity is the part it plays in the maintenance of posture. Posture is that nicety of adjustment between the various parts of the body to fit the new position taken as in sitting, standing, running, and reclining. In each position, the muscles must assume a new tonic state (posture) in addition to the more obvious contractions used for the change of position. Smooth continuity between normal movements in all kinds of muscular activity is dependent upon a mechanism which correlates these two types of response. When the position of the body changes, as during exercise, the tonus of its entire musculature must be modified so that each part may make a harmonious contribution to the activity as a whole. The importance of this postural or plastic tonus is indicated by the fact that when the underlying mechanism is disturbed the movements become incoördinated and ataxic.
Postural tonus depends upon the integrity of the reflex arcs and upon a steady but continuous bombardment of impulses into the muscles through the motor nerves from the central nervous system. An increase or decrease in the number of nerve fibers, and consequently the number of muscle fibers involved at any one time, leads to a greater or lesser state of tonic contraction. The afferent impulses upon which the posture of the body as a whole is dependent may arise in the muscles themselves (proprioceptors) or in the semicircular canals or from the cerebrum circuited through the cerebellum. Those from the muscles are influenced by the position of the parts with relation to the body as a whole, those from the semicircular canals by the position of the entire body in space. These are reinforced by the coördinating influence exerted by the cerebellum which also exercises or reinforces a general tonic effect. Thus, with the cord transected (spinal animal), an animal will have lost a large part of its power to maintain postural tonus. Simple myotatic reflexes are still present and are sufficient for certain simple movements of a reflex type. These are not adequate, however, for the maintenance of the postural tonus necessary for standing, walking, running, or support of the body.
There are two types of reaction which, when the proper stimuli arise, are accompanied by changes in postural tonus of the skeletal muscles. If one of a pair of antagonistic muscles normally employed in supporting the weight of the body against gravity is suddenly stretched, it responds with an increased development of tonus and comes to a new and shorter length. Its antagonist, on the other hand, is inhibited and comes to a new and greater length. Reflexes of this type involve the monomuscular are (myotatic reflex). In the other type of reaction the reverse is true. The tonus of the muscle may, from the same stimulus, give way almost suddenly. On releasing the tension applied, the muscle will be found to have taken on a new state of tonus and consequently a new length.
Just what conditions determine which response shall predominate is not known. The tension exerted by the muscles upon their points of insertion is maintained approximately constant. In progressive movements, as walking, postural adjustments must not only be made rapidly but with exactness. The stimulus which sets up a contraction of the extensors will inhibit the tonus existent in the flexors. A shortening reaction in one set of extensors is also associated with a simultaneous extending reaction in those of the opposite side or limb and vice versa. This condition is to be considered as an adaptation to the alternate responses which normally take place, as in walking and running. This kind of coördination is an example of reciprocal inhibition of opposite muscles and limbs.
Postural tonus depends upon the integrity of the reflex arcs and upon a steady but continuous bombardment of impulses into the muscles through the motor nerves from the central nervous system. An increase or decrease in the number of nerve fibers, and consequently the number of muscle fibers involved at any one time, leads to a greater or lesser state of tonic contraction. The afferent impulses upon which the posture of the body as a whole is dependent may arise in the muscles themselves (proprioceptors) or in the semicircular canals or from the cerebrum circuited through the cerebellum. Those from the muscles are influenced by the position of the parts with relation to the body as a whole, those from the semicircular canals by the position of the entire body in space. These are reinforced by the coördinating influence exerted by the cerebellum which also exercises or reinforces a general tonic effect. Thus, with the cord transected (spinal animal), an animal will have lost a large part of its power to maintain postural tonus. Simple myotatic reflexes are still present and are sufficient for certain simple movements of a reflex type. These are not adequate, however, for the maintenance of the postural tonus necessary for standing, walking, running, or support of the body.
There are two types of reaction which, when the proper stimuli arise, are accompanied by changes in postural tonus of the skeletal muscles. If one of a pair of antagonistic muscles normally employed in supporting the weight of the body against gravity is suddenly stretched, it responds with an increased development of tonus and comes to a new and shorter length. Its antagonist, on the other hand, is inhibited and comes to a new and greater length. Reflexes of this type involve the monomuscular are (myotatic reflex). In the other type of reaction the reverse is true. The tonus of the muscle may, from the same stimulus, give way almost suddenly. On releasing the tension applied, the muscle will be found to have taken on a new state of tonus and consequently a new length.
Just what conditions determine which response shall predominate is not known. The tension exerted by the muscles upon their points of insertion is maintained approximately constant. In progressive movements, as walking, postural adjustments must not only be made rapidly but with exactness. The stimulus which sets up a contraction of the extensors will inhibit the tonus existent in the flexors. A shortening reaction in one set of extensors is also associated with a simultaneous extending reaction in those of the opposite side or limb and vice versa. This condition is to be considered as an adaptation to the alternate responses which normally take place, as in walking and running. This kind of coördination is an example of reciprocal inhibition of opposite muscles and limbs.
Muscle tonus and its relation to posture
Extensibility and elasticity exist in muscle and are commonly known as the physical properties of muscle. By the former is meant that when a muscle is placed upon a stretch it is capable of being extended. This, however, does not obey Hooke's law, that is, the extension is not proportional to the opposing force, but with each increment of weight the extension becomes progressively less until a certain critical point is reached. Beyond this point the extensions become progressively greater with added increments until the muscle ruptures. The property of elasticity is that by which the muscle is capable of regaining its original length after being extended and when the strain is removed. The curve of elasticity is essentially the reverse of that of extension with the exception that the elastic recoil is not one-hundred per cent perfect. Both extensibility and elasticity are inherent properties of all varieties of muscle. These properties are greatly augmented during states of increased muscle tonus and when the muscle is contracting.
The physiological importance of the physical properties of muscle may be briefly summarized. They help to keep the muscles taut and thus prevent slack. This is essential for smoothness and freedom of movement of the bony levers. When a muscle first contracts against a lever, the inertia of that lever, especially if carrying a load, yields relatively slowly as compared to the rapid contractile phase of the muscle. It is obvious that the advantage of an extensible muscle would be to prevent rupture of that organ and to insure greater smoothness of movement. Contrast the result of trying to lift a weight quickly by means of a rigid wire and again by means of a strong but extensible body. Furthermore, in the action of antagonistic muscles, while one set is contracting the other must yield. This condition is made possible, in part, by the physical properties of muscle, but to a greater extent by muscle tonus. On the other hand, an extended antagonistic muscle, by means of its elasticity, may aid mechanically in bringing the moved part back to its original position.
During life the skeletal muscles are normally never in a complete state of rest. Even during sleep there is a slight continuous contraction. This state of tension which is maintained at some point between complete relaxation and complete contraction is known as simple musle tonus. During the waking hours this muscle tonus may be increased, but varies between wide limits from time to time and from muscle to muscle. The muscles may be considered as having taken on new elastic properties and will by virtue of this tend to assume greater or shorter lengths. Characteristic of muscle tonus is the fact that the tension exerted by the muscle on its points of origin and insertion tend to remain unchanged.
This tonus is not inherent in the muscle fibers themselves, but is dependent upon their connections with the central nervous system and reflex arcs. If the reflex are is broken at any point, as by cutting the afferent or efferent fibers of the dorsal and ventral roots, respectively, or by the destruction of the spinal cord, the muscles involved become toneless and flabby. Furthermore, in an animal with the spinal cord cut across, even when the afferent nerves leading from the adjacent muscles and from the skin are cut, thus leaving intact only those which arise in the muscle and tendon spindles (proprioceptive), simple muscle tonus persists. This definite highly localized monomuscular reflex has been clearly demonstrated and described by Sherrington, to which he has given the name myotatic reflex.
The adequate stimulus for this reflex is simple stretching, a stimulus which excites proprioceptors generally. This reflex is very exact and well graded. If only a part of the muscle is stretched that part only responds by a change of its tonus and the extent of this change is proportional to the strength of the stimulus (stretching). This local monomuscular effect may, however, be reinforced by impulses arising from other muscles in various parts of the body, from the semicircular canals, and from the cerebral and cerebellar portions of the brain. Pleasurable mental states as happiness, hope, and anticipation, are associated with a general increased tonus of the skeletal muscles. The jaw is held firm, the head and shoulders are erect, the eye is clear, and the step is firm. When one is mentally depressed, however, as from worry, fear, anxiety, and fatigue, the muscles are more flabby. The expression of the face is heavy, the eyes are dull with drooping eyelids, the facial muscles fall, and we speak of one being "down in the mouth." This condition of toneless muscles is incompatible with good health and proper functioning of the body.
The nature of the mechanism of skeletal-muscle tonus is still a moot question. Some workers hold that in these muscles are two types of muscle fibers, one of which is involved in the specific contractions and the other in the development of tonus. This seems quite unlikely since both the red and white muscle fibers, the two known types of fibers, have been shown to be contractile units and to respond similarly. A second viewpoint is that one and the same muscle fiber has an innervation from both the cerebrospinal and autonomic systems, the former initiating the specific responses, the latter having to do with tonus. The evidence to support this theory, however, all comes from negative experiments and is not at all conclusive. The safest viewpoint to accept seems to be that both specific contractions and tonus contractions are consummated by the same muscle fibers and innervated by the cerebrospinal nervous system only. This partial reaction is due to the fact that only a part of the muscle fibers are active at any one time. This state of activity in one given group of fibers and state of rest in other groups shifts by rotation. Such an explanation is in complete harmony with what we know of muscular contraction. Those fibers which are contracting at any one given time are doing so to the utmost of their ability ("all-ornothing" phenomenon), but they do not become fatigued since the burden is soon taken by another set which in turn is soon relieved, and so on. This would explain the fact that although muscle tonus is a reflex phenomenon it cannot be produced by artificial stimulation of either the afferent or efferent nerve trunks. To maintain muscle tonus, a relatively small expenditure of energy is required and only a small amount of heat is produced. Thus the intrinsic nature of muscle tonus is adapted to the rôle it has to play, namely, maintaining activity over extremely long periods of time.
The physiological importance of the physical properties of muscle may be briefly summarized. They help to keep the muscles taut and thus prevent slack. This is essential for smoothness and freedom of movement of the bony levers. When a muscle first contracts against a lever, the inertia of that lever, especially if carrying a load, yields relatively slowly as compared to the rapid contractile phase of the muscle. It is obvious that the advantage of an extensible muscle would be to prevent rupture of that organ and to insure greater smoothness of movement. Contrast the result of trying to lift a weight quickly by means of a rigid wire and again by means of a strong but extensible body. Furthermore, in the action of antagonistic muscles, while one set is contracting the other must yield. This condition is made possible, in part, by the physical properties of muscle, but to a greater extent by muscle tonus. On the other hand, an extended antagonistic muscle, by means of its elasticity, may aid mechanically in bringing the moved part back to its original position.
During life the skeletal muscles are normally never in a complete state of rest. Even during sleep there is a slight continuous contraction. This state of tension which is maintained at some point between complete relaxation and complete contraction is known as simple musle tonus. During the waking hours this muscle tonus may be increased, but varies between wide limits from time to time and from muscle to muscle. The muscles may be considered as having taken on new elastic properties and will by virtue of this tend to assume greater or shorter lengths. Characteristic of muscle tonus is the fact that the tension exerted by the muscle on its points of origin and insertion tend to remain unchanged.
This tonus is not inherent in the muscle fibers themselves, but is dependent upon their connections with the central nervous system and reflex arcs. If the reflex are is broken at any point, as by cutting the afferent or efferent fibers of the dorsal and ventral roots, respectively, or by the destruction of the spinal cord, the muscles involved become toneless and flabby. Furthermore, in an animal with the spinal cord cut across, even when the afferent nerves leading from the adjacent muscles and from the skin are cut, thus leaving intact only those which arise in the muscle and tendon spindles (proprioceptive), simple muscle tonus persists. This definite highly localized monomuscular reflex has been clearly demonstrated and described by Sherrington, to which he has given the name myotatic reflex.
The adequate stimulus for this reflex is simple stretching, a stimulus which excites proprioceptors generally. This reflex is very exact and well graded. If only a part of the muscle is stretched that part only responds by a change of its tonus and the extent of this change is proportional to the strength of the stimulus (stretching). This local monomuscular effect may, however, be reinforced by impulses arising from other muscles in various parts of the body, from the semicircular canals, and from the cerebral and cerebellar portions of the brain. Pleasurable mental states as happiness, hope, and anticipation, are associated with a general increased tonus of the skeletal muscles. The jaw is held firm, the head and shoulders are erect, the eye is clear, and the step is firm. When one is mentally depressed, however, as from worry, fear, anxiety, and fatigue, the muscles are more flabby. The expression of the face is heavy, the eyes are dull with drooping eyelids, the facial muscles fall, and we speak of one being "down in the mouth." This condition of toneless muscles is incompatible with good health and proper functioning of the body.
The nature of the mechanism of skeletal-muscle tonus is still a moot question. Some workers hold that in these muscles are two types of muscle fibers, one of which is involved in the specific contractions and the other in the development of tonus. This seems quite unlikely since both the red and white muscle fibers, the two known types of fibers, have been shown to be contractile units and to respond similarly. A second viewpoint is that one and the same muscle fiber has an innervation from both the cerebrospinal and autonomic systems, the former initiating the specific responses, the latter having to do with tonus. The evidence to support this theory, however, all comes from negative experiments and is not at all conclusive. The safest viewpoint to accept seems to be that both specific contractions and tonus contractions are consummated by the same muscle fibers and innervated by the cerebrospinal nervous system only. This partial reaction is due to the fact that only a part of the muscle fibers are active at any one time. This state of activity in one given group of fibers and state of rest in other groups shifts by rotation. Such an explanation is in complete harmony with what we know of muscular contraction. Those fibers which are contracting at any one given time are doing so to the utmost of their ability ("all-ornothing" phenomenon), but they do not become fatigued since the burden is soon taken by another set which in turn is soon relieved, and so on. This would explain the fact that although muscle tonus is a reflex phenomenon it cannot be produced by artificial stimulation of either the afferent or efferent nerve trunks. To maintain muscle tonus, a relatively small expenditure of energy is required and only a small amount of heat is produced. Thus the intrinsic nature of muscle tonus is adapted to the rôle it has to play, namely, maintaining activity over extremely long periods of time.
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