Elements of Physical Biology

Truth comes out of error more readily than out of confusion. —Bacon. A definition is a purely arbitrary thing. If I choose to define a triangle as a plane figure bounded by four sides and having four angles; and if, also, I define a quadrilateral as a plane figure bounded by three sides and having three angles, I shall run into no logical conflicts; my geometry need in no wise depart from that of Euclid; I shall need to make no changes in existing works on geometry, beyond that of substituting throughout the word triangle for the word quadrilateral, and vice versa.

But while a definition is in this sense, from the point of view of logic, a purely arbitrary thing, while my definition of a triangle as a four-sided figure may be admissible, it is by no means expedient. Thus the definition of terms, which naturally forms one of the first steps in the systematic treatment of any subject, may present no particular problems of logic, but it does present certain problems of expediency. In the geometrical example cited, the unusual definitions given, though quite permissible, are inexpedient for simple etymological reasons. Such a choice of terms would be misleading, and, instead of assisting the memory, would impose upon it an unnecessary burden. In this case the application of the principle of expediency is obvious to the point of being grotesque, the example having purposely been chosen to illustrate the principle in drastic fashion.

But the framing of definitions at times involves more subtle considerations of expediency, so subtle in fact, that they may be overlooked, or misunderstood, and a problem which is, in truth, a problem of definition, falsely masquerades as a problem of fact. Certain pseudo-problems of science have owed their origin to a failure to realize this circumstance.! 1 On the other hand, some very fundamental advances of science are, upon critical examination, found to rest essentially upon the establishment of a

The writer of the book of Genesis shows good judgment. Our legendary forebear, the originator of the first biological system of nomenclature, sees each creature first, and thereupon names it. We have not always been equally wise. Sometimes we have tried to invert the method; we have found or made a name, and then gaily set forth on an expedition to discover the thing that should answer to that name; we have hunted the Jabberwock. Forgetful of the wisdom of Mephistopheles:

Denn eben wo Gedanken fehlen Da stellt ein Wort zur rechten Zeit sich ein— we have given way to an inherent bias of the human mind described in characteristic fashion by H. G. Wells?: : when we have a name we are predisposed—and sometimes it is a very vicious predisposition—to imagine forthwith something answering tothename. . . . . If I say Wodget or Crump, you find yourself passing over the fact that these are nothings, . . . . and trying to think what sort of a thing a Wodget or a Crump may be. You find yourself insensibly, by subtle associations of sound and ideas, giving these blank terms attributes.®

So the biologist of the past generation, finding in his native vocabulary the words animal and plant, forthwith proceeded in an effort to establish precise distinctions between animals and plants, never giving any thought, it would seem, to the fact that these names had already been parceled out generations ago, by ‘popular’ consent, by unscientific persons without any regard to fine distinctions. There is clearly, here, the tacit assumption that because two distinct words are found in the vocabulary, therefore two correspondingly distinct things exist in nature. In point of fact, we know well enough (though we may not at all times have this knowledge clearly in the focus of our consciousness) that in nature many things form finely graded series, with extremes at the two ends, extremes to which

judicious definition. A notable instance of this is the enunciation of the principle of the survival of the fittest, which is essentially of the nature of a definition, since the fit is that which survives. Regarding the epistemological significance of definitions compare A. N. Whitehead and B. Russell, Principia Mathematica 1910, vol. 1, p. 12. 2H. G. Wells, First and Last Things, 1908, p. 32. * “Gewohnlich glaubt der Mensch, wenn er nur Worte hort, Es miisse sich dabei auch etwas denken lassen,’ Goethe.

our vocabulary has lent more or less definitely associated names, but , with no definite line of demarcation between. Examples of this are innumerable. We speak of objects as being red, orange, yellow, green, blue, violet, etc. There is nothing in nature to correspond to such staccato classification of colors: the visible spectrum runs continuously from a wavelength of about 8 x 10mm. (extreme red) to about 4 X 10-4 mm. (extreme violet). Cases therefore must necessarily arise when we are in doubt whether to call a thing blue, or green, for example; and such doubt can be resolved, if at all, only by arbitrary definition. The question is not ‘‘what zs green, and what zs blue,” but, at best, “what shall we agree to call green, and what blue.”

It lies in the nature of the mechanism by which we enter into possession of our knowledge, that problems of definition of this kind arise. We are equipped with two separate and distinct senses, the one responding to electromagnetic waves ranging from about 4 x 10+ to 8x 10+ mm., light waves; the other to somewhat longer waves otherwise of the same character, heat waves. Accordingly we have two separate terms in our language light and heat, to denote two phenomena which, objectively considered, are not separated by any line of division, but merge into one another by gradual transition. Here the question might be raised whether an electromagnetic wave of a length of 9 x 10-4 mm. is a light wave or a heat wave. The answer is obvious: Call it what you please, it is merely a question of arbitrary definition. We must beware of

as that false secondary power By which we multiply distinctions, then Deem that our puny boundaries are things Definitions in Biology. The attempt to establish a rigorous distinction between “animals” and “plants” may be similarly regarded. Expediency demands that if these terms are appropriated for exact scientific use, their sense, when so used, shall, if possible, be reasonably near akin to the sense commonly associated with these words. The difficulties encountered in seeking to establish a satisfactory line of division between animals and plants were long regarded as difficulties in a problem of fact. It was thought that some biological principle must be sought which divided animals from plants.

The truth is, of course, that we may define “animals” and “plants” any way we please—as for instance by reserving the term plant for an organism possessing cellulose—but whether such definition is “correct” or “satisfactory” is not a question of biological fact, it is a question of expediency. It is not a question whether there is any definable difference between animals as a class and plants as a class, nor what this difference is, but whether it is expedient to retain for purposes of strict scientific classification the popular terms “animals”’ and ‘‘plants,” which were not originally founded upon any rigorous examination of facts; and if so, where we should, by definition, draw the line of separation.

When the problem is viewed in this way the difficulty of distinguishing between animals and plants vanishes. In the case of the higher forms of life it is easy to establish biological distinctions that do not conflict with the popularly drawn lines of division. In the case of certain lowly forms of life popular distinctions cannot exist, since these forms are not known to the public except through biological publications. And the biological line of demarcation we can, by definition, draw arbitarily where we choose, or, better perhaps, we may say that the terms “animal,’’ “‘plant,’’ do not correspond to any fundamental objective distinction and, though conveniently applied to certain common forms of living matter, are entirely unnecessary‘ and only introduce difficulties of definition and classification when applied to certain simple organisms. What difference does it make whether we call Volvox a plant or an animal? Whether it zs a plant or an animal is merely a matter of definition, not a question of biological fact.

Somewhat similar remarks apply to the narrower divisions into which the biologist divides the world of living organisms. Disputes as to what constitutes a species are fruitless. ‘A species is a thing described as such.” This is simply a matter of definition. If on grounds of expediency one definition is preferable to another, it may be well to urge its general adoption. But its adoption or rejection will neither add nor subtract one jot from our stock of ascertained facts.

It is necessary to guard against the error of disputing about mere words. Not always does this error strut about in such blatant form as in the example quoted by Fechner: 8. Sachs, in a book published in 1850, takes the astronomers to task for their presumptuous speculations: “How do they know that the star they call Uranus is Uranus?” If any one should think that in our day it is no longer necessary to guard against errors of this kind (though less gross, perhaps), let him consider such a question as this: Is not the perennial debate between vitalism and mechanism a quibble about words? Is not the whole situation summed up accurately in the words of L. J. Briggs 35 “The mechanism of plant processes not at present explainable on a physico-chemical basis would be termed by the vitalistic school “vital,”’ by the physico-chemical school “unknown’’?

And in searching for the essential characteristics of life, those that should finally and conclusively distinguish the living from the nonliving, are we not just searching for the thing in nature that should correspond to a word in our vocabulary? Are we not hunting the Jabberwock? Definitions of Life. The difficulty of giving a precise meaning to the word life has been realized probably by everyone who has ever seriously attempted a definition. Herbert Spencer remarks:

Classifications are subjective concepts, which have no absolute demarcations in Nature corresponding to them . . . . Consequently, when we attempt to define anything complex . . . . we can scarcely ever avoid including more than we intended, or leaving out something that should be taken in. Thus it happens that on seeking a definition of life, we have great difficulty in finding one that is neither more nor less than sufficient. Nevertheless he proceeds to establish his definition of life: “The continuous adjustment of internal relations to external relations.’ It cannot be said that Spencer has been very happy in this choice of a definition or that he has been at all successful in avoiding the very pitfalls which he himself so clearly points out. For obviously many purely mechanical systems fall under this definition. It would, for example, include a windmill provided with a device automatically turning its arms into the most favorable plane according to the direction of the wind.? Indeed, in a sense it is true of every physical

7 Compare the following: ‘‘No one has yet succeeded in formulating a cleancut definition of the limits of the reflex either at its lower or its higher extreme, and perhaps no one ever will; for the whole list of behavior types, from machines to men, probably form a closely graded series.” C. J. Herrick: The Evolution of Intelligence and Its Organs. Science, 1910, vol. 31, p. 18. system that it “adjusts its internal relations to external relations.” For this statement simply implies that there is a tendency for the establishment of equilibrium between a selected portion of a physical system, and the remainder, the environment. Thus, for example, if the system 2H, + Oz is left to itself in a suitable vessel at 1480°C.8 = 5 which we may term an ‘Gnternal relation’ of the system, assumes the value 0.0002. If now the external conditions of temperature and pressure are changed

to 2929°C. and one atmosphere pressure, the internal relation 0 adjusts itself to the new external condition and acquires the value With better judgment than Herbert Spencer, Sir Edward Schifer® frankly evades the definition of life. He remarks: The ordinary dictionary definition of life is ‘‘the state of living.’”’ Dastre, following Claude Bernard, defines it as ‘‘the sum total of the phenomena common to all living beings.’? Both these definitions are, however, of the same character as Sidney Smith’s definition of an Archdeacon as ‘‘a person who performs archidiaconal functions.’’ I am not myself proposing to grapple with a task that has proved too great for the intellectual giants of philosophy, and I have the less inclination to do so because recent advances in knowledge have suggested the probability that the dividing line between animate and inanimate matter is less sharp than it has hitherto been regarded, so that the difficulty of finding an inclusive definition is correspondingly increased.

It is, indeed, an elementary historical fact that, as knowledge has advanced, the scope embraced in the term “‘vital’’ processes has continually decreased, since Wohler took the first cut out of it in 1828 by the synthesis of a “vital product” (urea) in the laboratory; and the field of known physico-chemical processes going on in living organisms has correspondingly increased. For the rest, the most uncompromising vitalist does not deny that some, at least, of the processes going on in living matter are physico-chemical. Even so fundamentally biological a process as the stimulation of an ovum to development we have learnt to effect by purely physical means.

Alleged Characteristics of Living Matter. On the other hand some of the features commonly ascribed to living matter as its peculiar *E. A. Schaefer, Presidential Address at Dundee Meeting of Brit. Assoc. Adv. Sci. 1912. and characteristic attributes seem irrelevant to the point of triviality. This remark applies particularly to the distinction sometimes claimed for living matter, that it grows “from within,’’ as distinguished from crystals, which, in a suitable mother liquor, “grow from without.” There may or may not be many and profound differences between a bacterial colony growing in a culture medium, on the one hand, and on the other hand a mass of crystals growing in a supersaturated solution. But whether the growth takes place from within or without is merely an accident of structure. If a droplet of chloroform is brought near to a glass particle coated with shellac, the drop flows around the particle, engulfs it, absorbs the shellac coating and finally rejects the ‘“‘undigested”’ glass particle.° The droplet thus grows “from within.”

In point of fact “growth from within” is the rule and not the exception in chemical systems. For what do we mean by growth? We mean the increase of the mass of one component of a system at the | expense of another. It is precisely the same thing as that which occupies the center of attention of the physical chemist, though he does not ordinarily call it growth. In fact, he does not find it necessary to give it any particular name, for, being accustomed to the use dm

d/m P of increase of mass with time, or, more often, aie ,rate of increase of concentration (mass/volume) with time. And in homogenous systems, at least, which (on account of their comparative ease of theoretical and experimental treatment) figure prominently in the physical chemistry of today, growth is necessarily from within. Some writers (J. Loeb, The Organism as a Whole, 1916, p. 28) have seen a characteristic feature, peculiar to living organisms, as distinguished, for example from crystals growing out of a solution,

10 “Tet it be clearly understood that this illustration is here quoted, not as an example of life-like analogies in the world of non-living matter; nor as a veiled suggestion that such a drop of chloroform represents even a modest degree of success in the artificial imitation of life; nor yet again as an argument that the conduct of amoeba can today be fully accounted for on a physicochemical basis; this example was cited merely to show that ‘growth from within” cannot be claimed as a distinguishing characteristic of living matter. For further discussion of so-called simulacra vitae see McClendon, Physical Chemistry of Vital Phenomena; Burns and Paton, Biophysics, 1921, p. 403.

in the fact that the latter grow by a physical process, the former by chemical processes. Leaving aside the question as to whether there exists any fundamental distinction between physical and chemical processes, at most the point to which attention is drawn by these authors would class living organisms with chemical, as distinguished from physical systems, but would furnish no basis whatever for separating organisms in a class by themselves from other chemical systems. This is not saying that they are not in a class by themselves, but only that the distinction suggested fails in effect.

It has similarly been urged, as a distinction between the growth of a crystal and that of an organism, that the former will grow only in a supersaturated solution of its own substance, while the latter extracts from an unsaturated solution the substance needed for its anabolism. This is really the same distinction in another form. It may distinguish the organism from the growing crystal, but leaves it in one class with any chemically reacting system whatever, since in the case of the latter also there is “‘growth,” i.e., formation of one or more products of reaction, in a system which need not be physically supersaturated in the narrow sense in which the crystallizing solution is. In a wider sense"! the system may indeed be said to be supersaturated with regard to a chemical substance that is formed within it—but in the same sense a system can probably be said to be supersaturated with regard to the substance of a bacterial colony growing therein.

Neither can we subscribe to the view set forth by J. Loeb (The Organism as a Whole, 1906, p. 29), that the synthesis of specific materials from simple compounds of non-specific character distinguishes living from non-living matter. In every chemical reaction specific materials are formed. In a mixture of hydrogen, chlorine, and nitrogen, the hydrogen and the chlorine unite, leaving the nitrogen on one side unchanged. ‘This is merely a brutally simple example of a universal fact. Chemical reaction is always selective. And if . “complexity” is to be made the characteristic of life processes, then the question immediately arises, what degree of complexity is required to place a given process in the category of life processes?

11 Namely in the sense that it is metastable, that is, its thermodynamic potential is not at a minimum. Reproduction. Another characteristic that has been cited by some as exclusively peculiar to living organisms is the power of reproducing their kind. ‘How’ says Driesch in effect,"can a mechanism provide for its own reconstitution? No machine known to us is able to construct another like itself, nor can it repair its own parts.”’!? Undue emphasis on this alleged distinction between living and nonliving machines seems ill advised, for two reasons. In the first place, though it may be true that no man-made engine exists that performs the functions of self-repair and self-reproduction, no one has ever attempted, so far as I know, to demonstrate that no such engine can be built. Anyone who should be disposed to regard this objection as specious should reflect for a moment on the amazing development in technical arts within the last thirty or forty years. Half a century ago one might with equal justice have pronounced flight a fundamental, essentially biological characteristic of birds, incapable of duplication by man-made engines.

But in another, perhaps more significant respect, we must regard as misplaced the emphasis sometimes laid on the power of reproduction in organisms, and its absence in human artefacts. It is based on an exaggerated conception of the part played by the parent in the making of the offspring. This probably has its origin in the instance of reproduction that to us is naturally of supreme interest, the reproduction of man. As a mammal, the young human organism grows within the parent body, and seems to us to be in some way fashioned by the parent; this conception must be at the basis of the alleged distinction between organic reproduction and the incapacity of non-living engines to reproduce their kind, for without such conception the comparison would lack all parallel. Now, in point of fact, we need but call to mind the familiar hatching of a chick to realize that the part necessarily played by the parent in the formation of the young individual is really very restricted. The process in this case goes on, for the most part, in complete isolation from the parent.

12H, C. Warren, Jour. Philos., Psychol. and Scientific Method, vol. 13, 1916, 18Compare E. G. Conklin, Heredity and Environment, 1918, pp. 99,45, 109: ‘“‘The hen does not produce the egg, but the egg produces the hen and also other eggs. . . . . We know that the child comes from the germ cells and not from the highly differentiated bodies of the parents, and furthermore that these cells are not made by the parents’ bodies but As for the initiation of cell division of the ovum, we now know that, in some cases at least, this can be effected by ordinary physical means.

Recent development in experimental embryology suggest a more rational view of this process of self-reproduction of the living engine, a view which strips it of at least some of its mystery, and which certainly takes from it any force it might otherwise have had as a basis for distinction between living and non-living matter. If, after the first division of the ovum of a frog, the two cells are separated, each will under suitable conditions develop into a separate and complete, normal organism. These two organisms A and B are, in fact twin brothers or sisters. No one would for a moment entertain the thought that in this case A reproduces B, or vice versa. Now suppose that in some way, after the first division, A alone grows into a complete mature organism, while the single cell B remains attached to it, say for six months. At the end of this time it is separated, and stimulated to start its growth into a frog. We would ordinarily describe this state of affairs by saying that A reproduced B as offspring, that B was the child of A. In point of fact it is merely a delayed twin brother or sister of its elder brother or sister A.“ A had little or nothing to do with the production of B; the latter grew, very much in the same way as A grew inits owntime. That nature has evolved, in surviving races, this method of delayed development, so as to stretch out the totality of living organisms in a long chain, a succession in time, is of course a fact of most fundamental importance, the significance of which will deserve our profound contemplation. One of its consequences has been to render possible a practically infinite number of organisms, built from a finite and quite restricted amount of matter, the same substance being used over and over again, for it is literally true that we live on our forefathers. Had all