Biophysics scope principles methods

The domain of discussion may be indicated by defining biophysics as the application to biological research of the methods and content of the physico-mathematical sciences. "Method" is advisedly placed first. It has become clear that the experimental and theoretical procedures usually associated with physics are not the exclusive property of that science, but represent rather adequately the developed and mature form of the scientific method itself. Biophysics is the adaptation of this methodology to the problems of biology.

It appears from this that the word "biophysics" is in part a misnomer. Biophysical research is biological research with a particular emphasis--concern for the logical ordering and quantification of biological theory, for the more intimate unification of theory and experiment, for the introduction into experimental biology of techniques and measuring devices which have been developed in the so-called physical sciences, and for the reduction-when it is possible and useful, and only then-of biological problems and concepts to already existent laws and concepts of the physical sciences.

That physics--the science of matter--has in fact preoccupied itself with those objects which used to be termed "non-living" is logically accidental, not intrinsic. Taken in this sense, the "physicalizing" of biology merely means the attempt to analyze certain complex phenomenal patterns in terms of somewhat simpler patterns which have already been the object of intensive study. In this sense it is neither novelty nor heresy, but an inevitable extension of the classical biological procedure of analyzing organisms into organs, organs into tissues, tissues into cells, and cells finally into their discernible parts.

It is only fair to add that "biophysics" is usually used in a sense which contrasts it with biochemistry--that is, as a study of the physical as distinct from the chemical aspects of biological systems. This viewpoint would see viscosity, osmotic pressure, surface tension, the electrical and mechanical properties of biological systems as physical, while the composition and metabolic activities of such systems are the concern of chemistry.

This criterion has been serviceable in the past, of course; but it is so narrow as to be both cramping to research and rather difficult rigidly to maintain. Thus, the study of bioluminescence must in this view separate sharply into two parts: the analysis of the luciferinluciferase system is biochemistry, while the emission of a photon by the reduced enzyme is biophysics. It is valid to say, "For the moment, let us consider only the physical aspects of this phenomenon, and ignore the chemical and purely biological." But the moment passes quickly, and the essential inseparability of the different aspects demands the broader interpretation.

It remains to consider the best way of subdividing biophysical activity into its branches according to some specified criterion of classification. From the preceding discussion it is clear that one apparently natural division-into theoretical and experimental--is not a desirable one. The nature of biophysics, as here defined, demands the same close interweaving, mutual support, and mutual stimulus of theorizing and experimenting as is now practised so successfully in physics.

To adopt the existing fundamentum divisionis of biology is no more desirable; for the fences around bacteriology, embryology, histology, physiology, botany, and the like, in view of their haphazard historical origin, exhibit small regard either for practical utility or for logical consistency. Some of these fields are organized around a particular function, some around a particular set of structures, some around a particular class of organisms, and some are mere catch-alls for topics which do not fit handily into the remaining cells.

If we accept the cell as fundamental concept in biology, a useful though by no means perfect mode of classification suggests itself--the hierarchy: cell-parts, cells, cell-aggregates. These further subdivide in a fairly natural way, principally according to functions and activities. Thus, under Cell-parts, we think of: Protoplasmic Structure; Enzyme Systems of the Cell; Nucleus and Chromosomes; Cell Membranes and Permeability; Golgi Bodies and Mitochondria.
Under Cells would come: Growth; Form; Motion; Division; Differentiation; Metabolism; Senescence; Stimulus-Response.

Under Cell-aggregates there are similar categories: Organic Form and Differentiation; Growth; Metabolism; Senescence; StimulusResponse. These would intersect with the triple classification: Tissues; Organs; Organisms. Thus, for example, we would find Secretion under Metabolism, Organs (perhaps also under Cells, Metabolism); special senses under Stimulus-response, Organs; and the nervous and endocrine systems under Stimulus-response, Organisms. Another category under Cell-aggregates would be Populations, which would cover the material of biometrics, ecology, and much of bacteriology.

Such a topic as The Virus is not an insuperable obstacle to this arrangement; there are many good reasons for placing it under CellParts. But it is obvious from the topics named that a better method than either equal-ranking classes or a hierarchy would be a multidimensional network, in which topics may be different distances apart, but in which each topic is linked to many others directly, and to all others indirectly. Protoplasmic Structure would be close to if not precisely at the centre of such network. With the further development of biophysics, the appropriate ordering will doubtless become more evident.

Applied biophysics is exceedingly scanty. There are a few scattered medical applications, such as the gold number or its modern equivalents in the analysis of cerebrospinal fluid, the use of X-rays and radium in the treatment of cancer. But biophysics is yet too young to show applications on any large scale.

There are many fields of biology in which the rather young biophysical method has not been active, so that a sufficient amount of representative material is not available for presentation. Some topics of biophysical interest, e.g., metabolism, are still referred to biochemistry for the same reason.