The science of life : fully illustrated in tone and line and including many diagrams

on Mars Beta life, an analogous thing and not the same thing. It may not be individualized ; it may not consist of reproductive individuals. It may simply be mobile. and metabolic. It is stretching a point to bring these two processes under one identical expression.

Moreover, if once we begin to speculate about the possibilities of something not exactly life as we know it, but analogous in its complexity or activity, to life, we are at liberty to entertain, so far as the sciences of chemistry and physics are concerned, a limitless variety of imaginary parallels. Life as we know it seems to be attached to and dependent upon, in ways we will presently investigate more fully, complex chemical compounds of carbon, nitrogen, hydrogen, oxygen, and other elements ; but we are really not limited to such compounds nor to the limiting temperatures and pressures within which they can play their parts, once we allow our minds to move beyond the life we actually know. We can conceive vaguely of silicon playing the part of carbon, sulphur taking on the réle of oxygen, and so forth, in compounds which, at a different tempo under pressures and temperatures beyond our earthly ken, may sustain processes of movement and metabolism with the accompaniment of some sort of consciousness, and even of individuation and reproduction. We can play with such ideas and evoke if we like a Gamma life, a Delta life, and so on through the whole Greek alphabet. We can guess indeed at subconscious and superconscious aspects to every material phenomenon. But all such exercises strain the meaning of the word life towards the breaking-point, and we glance at them only to explain that here we restrict our use of the word life to its common everyday significance of the individualized, reproductive, spontaneously stirring and metabolic beings about us.

In a recent survey of the whole universe known to physics, Sir J. H. Jeans, the brilliant secretary of the Royal Society, summarized the relation of life as we ordinarily conceive it to that universe in its entirety. ‘‘ The physical conditions,” he said, “‘ under which life is possible form only a tiny fraction of the range of physical conditions which prevail in the universe as awhole. The very concept of life implies duration in time; there can be no life where the atoms change their make-up millions of times a second and no pairs of atoms can ever become joined together. It also implies a certain mobility in space, and these two implications restrict

INTRODUCTION

life to the small range of physical conditions in which the liquid state is possible. Our survey of the universe has shown how small this range is in comparison with the range of the whole universe. Primeval matter must go on transforming itself into radiation for millions of millions of years to produce an infinitesimal amount of the inert ash on which life can exist. Even then this residue of ash must not be too hot or too cold, or life will be impossible. It is difficult to imagine life of any high order except on planets warmed by a sun, and even after a star has lived its life of millions of years, the chance, so far as we can calculate it, is still about a hundred thousand to one against its being a sun surrounded by planets. In every respect —space, time, physical conditions—life is limited to an almost inconceivably small corner of the universe.”

It is limited as yet, but it is still premature of us to define its final limitations. It seems that life must once have begun, but no properly informed man can say with absolute conviction that it will ever end.

§ 5 The Subjective Side of Life

One characteristic of life we have not yet noted. We know it directly only in our own individual cases ; we infer it in the life about us ; we suspect its extension to all life and perhaps even beyond the limits by which we have here defined life. This is feeling. We react to external stimulus, and we not only react but feel. Weare conscious and we have every reason to suppose that a great proportion at least of the living creatures about us are conscious too. When we see an oyster close its shell at the jabbing of a stick or a lobster search with its feet and pincers for a fragment of food, it seems natural to assume that these creatures also are feeling after the fashion in which we feel when we recoil from disagreeable or respond actively to agreeable sensations. We never experience any but our own feelings; all our belief in the feelings of other beings is based on the analogy of their movements to our own. We seem to detect shrinking and appetite even in the microscopic ameeba, and Sir Jagadis Chandra Bose, by a system of ingenious measurements, shows how even plants appear to be elated or depressed by the application of favourable or unfavourable substances, how they will seem to shudder at this or writhe at that in a fashion suggestive of feeling. But even a wire spring can be made to shudder at a

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