Elements of Physical Biology

these cells have arisen by the division of antecedent germ cells. Pd ig Parents do not transmit their characters to their offspring, but these germ cells in the course of long development give rise to adult characters similar to those of the parent.”’ ‘4'The perhaps somewhat doubtfully authenticated cases of fetus in fetu, “those strange instances in which one might almost say that a man may be pregnant with his brother or sister,’ add a touch of realism to the discussion here presented. For further data on this singular subject see G. M. Gould and W. L. Pyle, Anomalies and Curiosities of Medicine, 1897, pp. 199 et seq. Compare also in this connection, the phenomenon of pedogenesis; see for example, G. H. Parker, Psyche, 1922, vol. 29, p. 127.

these organisms sought to grow simultaneously, their career would have been stopped by lack of material. If anyone should object that these reflections leave out of account entirely the réle of sex in reproduction, with all the complex phenomena of the fusion of gametes, the mingling of chromosomes, and biparental inheritance, the obvious reply is that these phenomena are now known to be less fundamental than they formerly appeared; that reproduction of an organism can very well take place without them; and that therefore they may at most serve to distinguish certain forms of life from non-living matter, but they cannot possibly be made the basis of a distinction between living matter in general and that which we commonly describe as non-living.

Vital Force. If we have cause to hesitate in defining life, still more is it the part of wisdom to be very conservative in the coining and use of such phrases as vital force, nerve energy, and the like. Shall we not do well to follow the biblical example, and wait, to name the animal, until it is physically present to our senses? Or, to pass from legend to the world of scientific fact, let us borrow, if we can, | the method of the physicist: He discovers that a quantity 3 mv?

possesses certain important properties. Then, he proceeds to name it: Energy, in particular, kinetic energy. But biologists have been . disposed sometimes to adopt the reverse procedure: they have named a vital force, a nerve energy, a mental energy, and what not, and now they entertain the pious hope that in due time they may discover these “things.” That there is something radically at. fault with such terms is evident from the fact that forces and energy

are magnitudes, and “‘to define a magnitude and to say how it is , measured are one and the same thing.” But who has ever told us how to measure vital force!® and such like? Physical Chemistry of Structured Systems. In the physical chemistry of today structure, that is to say, geometrical configuration, plays a subordinate réle. For obvious reasons the theory of chemical reaction in homogeneous, or in heterogeneous systems of comparatively simple form, is more approachable than that of systems which possess intricate structure, resulting in complicated mechanical

16G, Bunge, in his Physiologic and Pathologic Chemistry, 1902, p. 1, remarks: “I regard vital force as a convenient resting place where, to quote Kant, ‘reason can repose on the pillow of obscure relations.’’’ Curiously enough this damning admission is made by an advocate of vitalism. interactions of their parts, in accompaniment of chemical reaction. In technical practise, too, reactions in homogeneous systems (solution, gas) are common, and where there is heterogeneous structure, this is usually of a form very simple as compared with the complex biological structures.

But this comparative absence, from physico-chemical discussion, of reference to structure, to geometrical features, is not due to any inherent characteristic property of chemical systems, as contrasted with the structurally complex organic systems: the reason for the simplicity is to be found in ourselves. It is not a physical phenomenon of the thing observed, but a psychological phenomenon in the observer. Physical chemistry is still a comparatively young science, and naturally the simpler phenomena have been sought out for first attention. This is not because complex physico-chemical structures do not exist, nor even because they are unimportant. On the contrary, it is to be expected that the future will bring important developments in this direction, as followed, for example by Sir William Bayliss in his work Interfacial Forces in Physiology.

The rate of formation, the rate of growth, of a chemical substance, is a definite function of its environment. In a structureless system the nature and state of this environment is defined in comparatively simple terms (e.g., by stating the concentration of each of the reacting substances). portion of the system depends on the structure, the topography of the system, which, in general, will be variable with the time. In particular, the structure may be such that a given substance or complex of substances carries its own immediate environment around with it. The rate of formation (growth) of that substance will then depend largely upon the mechanical properties of those portions of the system which accompany this substance or complex in its travels through the system.

The complete discussion of a system of this kind may well fall outside the scope of present day physical chemistry, not because it is inherently foreign to that branch of science, but because no case of this kind, sufficiently simple to invite discussion on a mathematical and physico-chemical basis, has clearly presented itself.17 ‘7 Compare W. M. Bayliss, Physiology, 1915, p. XI, ‘All that we are justified in stating is that, up to the present, no physico-chemical system has been

Yet there is absolutely nothing in such a case that in principle places it outside the pale of physico-chemical science. It is largely as the result of intentional selection of simple conditions that the systems with which the chemist ordinarily deals (outside of biological chemistry) are comparatively structureless. We can, in fact, even now lay down certain general observations with regard to structured physico-chemical systems. Let us consider a system of this kind in which local conditions are subject to variation from point to point and from instant to instant. We fix our attention on some one component which requires for its growth certain definite conditions of its immediate environment. If this component is associated with a structure whose geometrical and mechanical properties secure and maintain for it a comparatively constant suitable environment amid the changing conditions of the system, then that component will grow.

Furthermore, the several components will compete with greater or less success for the material available for their growth, in proportion as their structure is more or less perfectly adapted to secure and maintain for them a suitable environment. The chemical dynamics of such a system, that is to say, the laws governing the distribution of matter among its several components, may evidently assume a fundamentally different character from that to which we are accustomed from our study of ordinary structureless systems. For in these latter the arrangement and rearrangement of matter within the system depends chiefly on chemical coefficients (affinity coefficients), and scarcely at all on geometrical features.

In structured systems, on the other hand, there is the possibility that geometrical and mechanical features may play the dominant role. This possibility will present itself particularly in those systems which receive a continuous or periodic supply of free energy, for instance in the form of illumination. Here the advantage will go to those structures that are adapted to direct available energy into such | channels as lead to the maintenance of the environment required for their | growth.8 Buta little reflection shows that this is precisely the princi- |

met with having the same properties as those known as vital; in other words, none have, as yet, been prepared of similar complexity and internal coordination. 18 It should be observed that nothing has been said of life in describing the system. The system may or may not comprise living organisms, the argument. ple which governs survival in the struggle for existence among living organisms. Hence we may say: The laws of the chemical dynamics of a structured system of the kind described will be precisely those laws, or at least a very important section of those laws, which govern the evolution of a system comprising living organisms.

For it is precisely structured systems of the kind considered above that are presented to us in living organisms growing in an “environment.” Application to Biology. The several organisms that make up the earth’s living population, together with their environment, constitute one system,!® which receives a daily supply of available energy from the sun. Each individual is composed of various chemical substances assembled into a definite structure and capable of growth, i.e., of accretion out of the environment by chemical reaction—provided a suitable medium or environment is offered.

Moreover, each mobile organism carries with it a travelling environment, suitable for the growth of its substance. It maintains this environment by virtue of the peculiar mechanical properties associated with its structure, whereby it is enabled to turn to this use, directly or indirectly, the available energy of the sun’s light. And while the travelling environment may not be absolutely constant, remains the same. This suggests that a term, such as life, so vague that it defies definition, is perhaps not likely to play an important part in any exact argument; we may, indeed, find it wholly unnecessary. It may, in time, in the literature of exact science, meet with the fate of the word cause: a term of rare and at best incidental occurrence in records of exact investigations.

19 This fact deserves emphasis. It is customary to discuss the ‘‘evolution of a species of organisms.’’ As we proceed we shall see many reasons why we should constantly take in view the evolution, as a whole, of the system [organism plus environment]. It may appear at first sight as if this should prove a more complicated problem than the consideration of the evolution of a part only of the system. But it will become apparent, as we proceed, that the physical laws governing evolution in all probability take on a simpler form when referred to the system as a whole than to any portion thereof.

| It is not so much the organism or the species that evolves, but the entire system, species and environment. The two are inseparable. “The organism, as Uexkiill teaches us, must be studied, not as a congeries of anatomical and physiological abstraction, but as a piece of machinery, at it is more nearly so than the more remote portions of the system, and keeps within such limits of variation as are compatible with the survival of the organism or its species. A concrete illustration may help to make this point clear. Many aquatic forms of life are constantly bathed in a saline solution—sea water. Their body fluids are accordingly in equilibrium with this environment. Variations in the salinity of their environment, if they exceed certain comparatively narrow bounds, are apt to be fatal to such organisms.

The higher organisms have made themselves (largely) independent of their immediate environment. Their tissues are bathed from within by a fluid (the blood) which they carry around with them, a sort of ‘internal environment.’’?° The degree of perfection with which this constancy of the internal or traveling environment, independently of the external environment, is developed, increases as we ascend the biologie scale. This is lucidly set forth, for example, by Claude Bernard :?!

Chez tous les étres vivants le milieu intérieur qui est un produit de l’organisme, conserve les rapports nécéssaires d’échange avec le milieu éxtérieur; mais & mesure que |’organisme devient plus parfait, le milieu organique se spécifie et s’isole en quelque sorte de plus en plus du milieu ambiant. It is the peculiar structure and the mechanical properties of the organism that enable it to secure and maintain the required environment (including the milieu intérieur). The higher animals, in particular, are provided with an intricate apparatus, comprising many members, for securing food (internal environment) as well as for warding off hostile influences.

20 “‘Fitant donné que |’eau de mer a un contact si intime avec les organismes de la mer et que non seulement elle les entoure de ses flots, mais qu’elle traverse leurs branchies et imprégne en partie les corps des invertébrés, il semble assez justifié de la placer dans la méme catégorie que les autres liquides physiologiques.”’ S. Palitzsch, Comptes Rendus de Carlsberg, vol. 10, part 1, 1911, p. 93. Compare also the following: “Not only do the body fluids of the lower forms of marine life correspond exactly with sea water in their composition, but there are at least strong indications that the fluids of the highest animals are really descended from sea water . . . . the same substances are present in both cases, and in both cases sodium chloride largely predominates.” L. J. Henderson, The Fitness of the Environment, 1913, pp. 187-188. See also ibid., pp. 116 and 153; H. F. Osborn, The Evolution and Origin of Life, 1917, p. 37; D’Arcy W. Thompson, Growth and Form, 1917, p. 127.

The increasing independence, as we ascend the biological scale, which the organism displays toward its more remote environment, is thus accompanied by a parallel increase in the perfection of the apparatus by which this independence is earned. Here again we may quote Claude Bernard:”? A mesure que |’on s’éléve dans |’échelle des étres, ces appareils deviennent plus parfaits et plus compliqués; ils tendent a affranchir complétement Vorganisme des influences et des changements survenus dans le milieu ex- térieur. Chez les animaux invertébrés, au contraire, cette independence vis- a-vis du milieu extérieur n’ est que relative.

The Policy of Resignation: Its Parallel in Other Sciences. Whatever may be our ultimate conclusions, we may do well to adopt at least as a temporary expedient the policy of resignation; with Sir Edward Schifer we may abandon the attempt to define life. Perhaps, in doing this, we are following historical precedents: Geometers have had to resign themselves to the fact that Euclid’s parallel axiom cannot be proved. But as the reward of this resignation came the new geometries of Bolyai, Lobatchewski and Riemann. Enlightened inventors have abandoned the attempt to build a perpetual motion machine; but again, resignation is rewarded with the recognition of a fundamental law, the law of conservation of energy. Physicists, following Einstein, have abandoned, for the time being at any rate, the attempt to determine experimentally the earth’s absolute motion through space. The reward has been the theory of relativity, one of the greatest events in the history of science.

The whole development of science, especially in recent years, is a record of tearing down barriers between separate fields of knowledge and investigation. Little harm, and perhaps much gain, can come from a frank avowal that we are unable to state clearly the difference between living and non-living matter. This does not in any way commit us to the view that no such difference exists. For the present, then, we shall adopt the position that the problem is essentially one of definition. The question is not so much “What is life,” but rather, “What shall we agree to call life?” And the answer, for the present at any rate, seems to be that it is immaterial how we define life; that the progress of science and our understanding of natural phenomena is quite independent of such a definition.

We shall, wherever convenient, continue to employ the terms life, living organism, merely as a matter of convenience. This use of the terms does not imply or presuppose any precise distinction between living and non-living matter; it merely rests upon the fact that in most cases ordinarily met there is essentially universal agreement as to whether a portion of matter is to be classed in the first or in the second category. We will adopt the policy of Sir William Bayliss:

If asked to define life I should be inclined to do as Poinsot, the mathematician did, as related by Claude Bernard: “If anyone asked me to define time, I should reply: Do you know what it is that you speak of? If he said Yes, I should say, Very well, let us talk about it. If he said No, I should say, Very well, let us talk about something else.”’ The ideal definition is, undoubtedly, the quantitative definition, one that tells us how to measure the thing defined; or, at the least, one that furnishes a basis for the quantitative treatment of the subject to which it relates. We have already spoken of evolution. Most of what follows will relate directly or indirectly to evolution. It will be well here, while discussing definitions, to establish a definition, a conception, of evolution that shall, as far as may be, have the quantitative stamp.

Nature must be considered as a whole if she is to be understood in detail. —Bunge. As has been abundantly made plain, the choice of a definition is amatter of expediency. In adopting, for special use in exact science, a term already in general use, we must seek, so far as possible, to embody in our definition the fundamental and essential features of the concept denoted by the term as used popularly and by the best workers, thinkers and writers.1_ In so far as there is divergence in the use of the term, it may be well to frame the definition broadly, so as to cover a wide range of phenomena and lead to a comprehensive view of natural events, corresponding to the essential unity of nature. In this way we shall be most likely to see the facts of nature arraying themselves in a natural order, and to achieve that economy of thought which is secured by a well devised system of classification. Facts which naturally belong together will, then, be found together, in our system, in the same or in neighboring pigeonholes.

Now if we seek to analyze what is in our minds when we speak of the evolution of a given system, we find—and on this probably all are agreed—that the fundamental, the central thought, is that of the history of the system. But the concepts of the history and of the evolution of a system, though related, are not identical—if they were, one word would suffice to denote the single concept. The popular and also the scientific conception of evolution contains as an essential feature the element of progress, of development. We would not ordinarily class as evolution the history of such a system as a swinging pendulum, or a celestial body circling in its orbit, in so far

‘ Compare Bertrand Russell, Analysis of Mind, 1921, p. 197: ‘‘The use of the word comes first, and the meaning is to be distilled out of it by observation and analysis.’”” ‘In each case the work consists chiefly in making explicit processes which are instinctive,’ as J. W. N. Sullivan (Aspects of Science, 1923, p. 24) remarks Apropos of certain other matters. as these motions are purely periodic or cyclic. In the history of such systems the element of progression in time, of development, is lacking. They repeat in endless succession the same series of events. The hand of the clock, like a symbol of perpetual youth, goes through its daily double cycle, making no distinction between yesterday, today and tomorrow. It is the calendar that reminds us we grow older year by year, the calendar that turns a new and different leaf each day. “The book of Nature is the book of Fate. She turns the gigantic pages—leaf after leaf, never returning one. . . . . 7

But, to characterize the kind of history we speak of as evolution, it is not enough that each day be unlike every other; it is not merely that a system never passes twice through the same state;3not merely that a biological species never retraces its steps, or that ‘‘when a © race has lived its term it comes no more again.’ Evolution not a Mere “‘Changeful Sequence.”’ Such a statement as those cited in the preceding paragraph alone is insufficient to distinguish evolution as a progress from merely a changeful sequence; it is insufficient to define the direction of evolution.’ For if the world’s events taken in historical order A, B, C .. . area changeful sequence, the same is also true of the inverted series

C, B, A. Mere unlikeness of two days is insufficient to tell us which is antecedent to the other. To determine this we must know something regarding the character of the unlikeness. In a vague way this character is indicated by the term progress, which, as already remarked, is closely associated, in popular conception, with evolution. And the more rigorous scientific disciplines of biology, too, leave us with a not very clearly defined idea of progression as one of the fundamental characteristics of those changes which are embraced by the term evolution. Such phrases as “the passage from lower to higher forms” which are often used to describe the direction of evolution, are vague, and