LIFE: ITS NATURE, ORIGIN, AND MAINTENANCE.1

By E. A. SCHÄFER, LL.D., D.Sc., M.D., F.R.S.,

Professor of Physiology in Edinburgh.

PREFACE.

In the following essay, which formed the presidential address to the British Association at its meeting in Dundee in 1912, I have tried to indicate in clear language the general trend of modern biochemical inquiries regarding the nature and origin of living material and the manner in which the life of multicellular organisms, especially that of the higher animals and man, is maintained. I have also stated the conclusions which it appears to me may legitimately be drawn from the result of those inquiries, without ignoring or minimizing such difficulties as these conclusions present.

There is, it may be admitted, nothing new in the idea that living matter must at some time or another have been formed from lifeless material, for in spite of the dictum omne vivum e vivo, there was certainly a period in the history of the earth when our planet could have supported no kind of life, as we understand the word; there can, therefore, exist no difference of opinion upon this point among scientific thinkers. Nor is it the first time that the possibility of the synthetic production of living substance in the laboratory has been suggested. But only those who are ignorant of the progress which biochemistry has made in recent years would be bold enough to affirm that the subject is not more advanced than in the days of Tyndall and of Huxley, who showed the true scientific instinct in affirming a belief in the original formation of life from lifeless material and in hinting at the possibility of its eventual synthesis, although there was then far less foundation upon which to base such an opinion than we of the present day possess. The investigations of Fischer, of Abderhalden, of Hopkins, and of others too numerous to mention, have thrown a flood of light upon the constitution of the materials of which living substance is composed; and, in particular, the epochmaking researches of Kossel into the chemical composition of nuclear

1 An address delivered to the British Association for the Advancement of Science, at its meeting at Dundee in September, 1912. Reprinted by permission from pamphlet copy printed by Longmans, Green & Co., London, 1912.

substance-which in certain forms may be regarded as the simplest type of living matter, while it is certainly the fons et origo of all active chemical processes within most cells-have shown how much less complex in chemical nature this substance may be than physiologists were a few years ago accustomed to regard it. On this and other grounds it has lately been independently suggested by Prof. Minchin that the first living material originally took the form, not of what is commonly termed protoplasm, but of nuclear matter or chromatin: a suggestion which appears by no means improbable.

If the honored names of Charles Darwin, Ernst Häckel, and August Weismann are not found in the following pages, it is because exigencies of space and time rendered it necessary to deal mainly with the more modern developments of this chapter of evolutionary history. For other but not less cogent reasons all metaphysical speculations on the subjects dealt with have been avoided. The study of natural knowledge, as the Royal Society still quaintly describes in its title the investigation of the phenomena of nature, is never properly advanced if mixed up with the "supernatural" or if metaphysics is appealed to for the explanation of scientific problems which can not at once be solved by ordinary scientific methods; and it behooves us to eliminate all considerations involving the intervention of superantural agencies just as much in connection with scientific inquiries into the nature and origin of life as with all other matters which are properly the subject of scientific investigation. This is not materialism, but

common sense.

The first part of the subject of this address is dealt with at considerable length and in a strictly scientific spirit by Le Dantec in "The Nature and Origin of Life," as well as by Dastre in the book mentioned on the next page. To works such as these the reader is referred for the numerous details which it is impossible to include within the limits of a short essay.

DEFINITION.

Everybody knows, or thinks he knows, what life is; at least we are all acquainted with its ordinary, obvious manifestations. It would therefore seem that it should not be difficult to find an exact definition. The quest has, nevertheless, baffled the most acute thinkers. Herbert Spencer devoted two chapters of his "Principles of Biology" to the discussion of the attempts at definition which had up to that date been proposed, and himself suggested another. But at the end of it all he is constrained to admit that no expression had been found which would embrace all the known manifestations of animate, and at the same time exclude those of admittedly inanimate, objects.

The ordinary dictionary definition of life is "the state of living.” Dastre, following Claude Bernard, defines it as "the sum total of

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the phenomena common to all living beings." Both of 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 take up your time by attempting to grapple with a task which has proved too great for the intellectual giants of philosophy, and I have the less disposition 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. As a mere word "life" is interesting in the fact that it is one of those abstract terms which has no direct antithesis, although probably most persons would regard "death" in that light. A little consideration will show that this is not the case. "Death" implies the preexistence of "life." There are physiological grounds for regarding death as a phenomenon of life—it is the completion, the last act of life. We can not speak of a nonliving object as possessing death in the sense that we speak of a living object as possessing life. The adjective "dead" is, it is true, applied in a popular sense antithetically to objects which have never possessed life, as in the proverbial expression "as dead as a doornail." But in the strict sense such application is not justifiable, since the use of the terms "dead" and "living" implies either in the past or in the present the possession of the recognized properties of living matter. On the other hand, the expressions living and lifeless, animate and inanimate furnish terms which are undoubtedly antithetical. Strictly and literally the words "animate" and "inanimate" express the presence or absence of "soul," and not infrequently we find the terms "life" and "soul" erroneously employed as if identical. But it is hardly necessary for me to state that the remarks I have to make regarding "life" must not be taken to apply to the conception to which the word "soul" is attached. The fact that the formation of such a conception is only possible in connection with life, and that the growth and elaboration of the conception has only been possible as the result of the most complex processes of life in the most complex of living organisms has doubtless led to a belief in the identity of life with soul. But unless the use of the expression "soul" is extended to a degree which would deprive it of all special significance, the distinction between these terms must be strictly maintained. For the problems of life are essentially problems of matter; we can not conceive of life in the scientific sense as existing apart from matter. The phenomena of life are investigated, and can only be investigated, by the same methods as all other phenomena of matter, and the general results of such investigations tend to

1 La vie et la mort, English translation by W. J. Greenstreet, 1911, p. 54.

show that living beings are governed by laws identical with those which govern inanimate matter. The more we study the manifestations of life the more we become convinced of the truth of this statement and the less we are disposed to call in the aid of a special and unknown form of energy to explain those manifestations.

PHENOMENA INDICATIVE OF LIFE-MOVEMENT.

The most obvious manifestation of life is "spontaneous" movement. We see a man, a dog, a bird move, and we know that they are alive. We place a drop of pond water under the microscope, and see numberless particles rapidly moving within it; we affirm that it swarms with "life." We notice a small mass of clear slime changing its shape, throwing out projections of its structureless substance, creeping from one part of the field of the microscope to another. We recognize that the slime is living; we give it a name Amaba limaxthe slug amoeba. We observe similar movements in individual cells of our own body; in the white corpuscles of our blood, in connective tissue cells, in growing nerve cells, in young cells everywhere. We denote the similarity between these movements and those of the amoeba by employing the descriptive term "amoeboid" for both. We regard such movements as indicative of the possession of "life"; nothing seems more justifiable than such an inference.

But physicists' show us movements of a precisely similar character in substances which no one by any stretch of imagination can regard as living; movements of oil drops, of organic and inorganic mixtures, even of mercury globules, which are indistinguishable in their character from those of the living organisms we have been studying: movements which can only be described by the same term amœboid, yet obviously produced as the result of purely physical and chemical reactions causing changes in surface tension of the fluids under examination. It is therefore certain that such movements are not specifically "vital," that their presence does not necessarily denote "life." And when we investigate closely, even such active movements as those of a vibratile cilium or a phenomenon so intimately identified with life as the contraction of a muscle, we find that these present so many analogies with amoeboid movements as to render it certain that they are fundamentally of the same character and produced in much the same manner. Nor can we for a moment doubt that the

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1 G. Quincke, Annal. d. Physik u. Chem., 1870 and 1888.

The causation not only of movements but of various other manifestations of life by alterations in surface tension of living substance is ably dealt with by A. B. Macallum in a recent article in Asher and Spiro's Ergebnisse der Physiologie, 1911. Macallum has described an accumulation of potassium salts at the more active surfaces of the protoplasm of many cells, and correlates this with the production of cell activity by the effect of such accumulation upon the surface tension. The literature of the subject will be found in this article.

G. F. Fitzgerald (Brit. Assoc. Reports, 1898, and Scient. Trans. Roy. Dublin Society, 1898) arrived at this conclusion with regard to muscle from purely physical considerations.

complex actions which are characteristic of the more highly differentiated organisms have been developed in the course of evolution from the simple movements characterizing the activity of undifferentiated protoplasm; movements which can themselves, as we have seen, be perfectly imitated by nonliving material. The chain of evidence regarding this particular manifestation of life-movementis complete. Whether exhibited as the amoeboid movement of the proteus animalcule or of the white corpuscle of our blood; as the ciliary motion of the infusorian or of the ciliated cell; as the contraction of a muscle under the governance of the will, or as the throbbing of the human heart responsive to every emotion of the mind, we can not but conclude that it is alike subject to and produced in conformity with the general laws of matter by agencies resembling those which cause movements in lifeless material.1

ASSIMILATION AND DISASSIMILATION.

It will perhaps be contended that the resemblances between the movements of living and nonliving matter may be only superficial, and that the conclusion regarding their identity to which we are led will be dissipated when we endeavor to penetrate more deeply into the working of living substance. For can we not recognize along with the possession of movement the presence of other phenomena which are equally characteristic of life and with which nonliving material is not endowed? Prominent among the characteristic phenomena of life are the processes of assimilation and disassimilation, the taking in of food and its elaboration. These, surely, it may be thought, are not shared by matter which is not endowed with life. Unfortunately for this argument, similar processes occur characteristically in situations which no one would think of associating with the presence of life. A striking example of this is afforded by the osmotic phenomena presented by solutions separated from one another by semipermeable membranes or films, a condition which is precisely that which is constantly found in living matter.

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It is not so long ago that the chemistry of organic matter was thought to be entirely different from that of inorganic substances.

1 "Vital spontaneity, so readily accepted by persons ignorant of biology, is disproved by the whole history of science. Every vital manifestation is a response to a stimulus, a provoked phenomenon. It is unnecessary to say this is also the case with brute bodies, since that is precisely the foundation of the great principle of the inertia of matter. It is plain that it is also as applicable to living as to inanimate matter."-Dastre, op. cit., p. 280.

The terms "assimilation" and "disassimilation" express the physical and chemical changes which occur within protoplasm as the result of the intake of nutrient material from the circumambient medium and its ultimate transformation into waste products which are passed out again into that medium; the whole cycle of these changes being embraced under the term "metabolism."

* Leduc (The Mechanism of Life, English translation by W. Deane Butcher, 1911) has given many illustrations of this statement. In the report of the meeting of 1867 in Dundee is a paper by Dr. J. D. Heaton (On Simulations of Vegetable Growths by Mineral Substances) dealing with the same class of phenomena. See also J. Hall-Edwards, Address to Birmingham and Midland Institute, November, 1911. The conditions of osmosis in cells have been especially studied by Hamburger (Osmotischer Druck und Ionenlehre, Wiesbaden, 1902-4).