In contrast with the cosmic earthquake that the study of physics underwent in the years before 1930, change moved tranquilly in the fields of biology and chemistry. Indeed in biology most of the work of the 1920's continued along lines already established in the nineteenth century.
In genetics, the key event was the rediscovery in 1900 of the work of the Bohemian monk Gregor Mendel, who, contemporaneously with the later researches of Darwin in the 1860's, conducted the epoch-making experiments with the crossbreeding of peas that were to form the basis of the whole modern study of inheritance. The most significant outcome of Mendel's discoveries was the identification of indivisible and unalterable units called genes, through whose infinitely varied combination the process of heredity proceeded. This genetic theory seriously undermined Darwin's principle of natural selection. Some geneticists were ready to discard natural selection entirely, some preferred to retain it in modified form, but there was general agreement that acquired characteristics were not inherited. Mendel's original conclusions were reinforced when twentieth-century geneticists began to extend his work to systematic experiments with the fast-reproducing fruit fly, and to apply the calculus of probabilities to their findings. As a result, by the 1920's the new science of genetics had reached a high level of technical exactitude. Moreover, in treating the gene as a basic and indivisible unit, it seemed to confirm Planck's contention that nature proceeded by jumps and in definite quantities rather than through the continuous and imperceptible processes of change that had been postulated by nineteenth-century philosophers of nature.
Another link between biology and the theory of physics was provided by the new science of biophysics, which, along with the related field of biochemistry, accounted for a large part of the progress made in the study of the human body. Perhaps the most dramatic experiments were those of Sir Frederick Gowland Hopkins in 1912, which became the starting point for the systematic investigation of nutrition and the identification of the basic vitamins. For a long time the chemistry of all the vitamins except D remained a mystery. But in 1929, with the chemical breakdown of Vitamin A, there began a period of rapid progress in the analysis and synthetic production of these substances that continued down to the outbreak of the Second World War.
Closely related to this study was the development of the new science of glands and internal secretions known as endocrinology. In the 1920's, the function of hormones began to be understood, and work on the pituitary and thyroid glands proceeded steadily. Discoveries such as these obviously had relevance for medicine. Indeed, a salient characteristic of the decade was that now, for the first time in history, new research in physiology and biochemistry was quickly applied in clinical practice. An astounding advance resulted. In the mid-1920's there began a period of breathtaking innovation that brought more progress in medicine in a single generation than the profession had known in all previous human history.
The discovery of antitoxins, begun in the 1890's, moved on steadily, as did the analysis of the corresponding viruses. By this method, medical research succeeded in eliminating certain diseases almost completely: as smallpox had been routed in the nineteenth century, so the conquest of diphtheria, yellow fever, and tetanus followed in the interwar period. But most diseases resisted this sort of immunization. Although the ravages of tuberculosis, for instance, were enormously reduced, no satisfactory antitoxin was discovered to combat it. In dealing with these stubborn diseases, the development of antibiotics marked the crucial turning point. Beginning with Sir Alexander Fleming's almost accidental discovery of penicillin in 1928, one new drug followed another in a rapid sequence of successful experiments leading to commercial production.
In all these cases, however, there had been a time lag between laboratory research and its clinical application. Not until the Great Depression had focused attention on problems of hunger and want were the new discoveries in the field of nutrition and vitamins fully exploited. Through the necessities of treating vast masses of sick and wounded soldiers in the Second World War, penicillin, the sulfa drugs, and DDT came into their own. These examples suggest the close relationship between social needs and the development of scientific and medical knowledge in our time.
Similarly, in the organization of research, economic and social factors began to exert an increasingly important influence. In the past, the isolated scientist or physician could produce useful and even epoch-making results with the simple equipment of his own home laboratory. By the 1920's, only a wellfurnished laboratory or research institute could contribute to the growth of scientific knowledge. With this change, the problem of the organization and financing of research took on a new urgency. In such respects, a large and wealthy society like that of the United States enjoyed obvious advantages; a socialized country, such as the Soviet Union, held potential assets for the future. Thus even as early as the 1920's, men of science in the three countries that together had accounted for most of the scientific progress of the nineteenth century--Britain, Germany, and France--were beginning to wonder whether the economy and the way of life that had yielded such marvelous results a generation or two earlier, would prove capable of dealing with the unfamiliar and pressing demands of twentieth-century mass society.
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