The biological explanation of a jumping bean is sometimes felt to be puzzling, inasmuch as the creature is wholly enclosed; and a man in a boat knows that he cannot propel it by movement inside, without touching the water or something external. But the reaction of a table can be made use of through the envelope, and a live thing can momentarily vary its own weight-pressure and even reverse its sign. This fact has a bearing on some psycho-physical experiments, and hence is worthy of a moment's attention.
To weigh an animal that jumps and will not keep still is always troublesome. It cannot alter its average weight, truly, but it can redistribute it in time; at moments its apparent weight may be excessive, and at other moments zero or even negative, as during the middle of an energetic leap. Parenthetically we may here interpolate a remark and say that what is called interference of light (two lights producing darkness, in popular language) is a redistribution of luminous energy in space. No light, nor any kind of wave motion, is destroyed by interference when two sets of waves overlap, but the energy rises to a maximum in some places, and in other places sinks to zero. No wave energy is consumed by interference—only rearranged. This fact is often misstated. And probably the other statement, about the varying apparent weight—i.e. pressure on the ground—of a live animal, may be misstated too: though there is no question of energy about that, but only of force. The force or true weight, in the sense of the earth's attraction, is there all the time, and is constant; but the pressure on the ground, or the force needed to counteract the weight, is not constant. After momentary violence, as in throwing, no support need be supplied for several seconds; and, like the maggot inside a hollow bean, a live thing turning itself into a projectile may even carry something else up too. It is instructive also to consider a flying bird, and a dirigible balloon, and to ask where the still existing weight of these things can be found.
Note B.—Differences between a Growing Organism and a
Growing Crystal
The properties which differentiate living matter from any kind of inorganic imitation may be instinctively felt, but can hardly be formulated without expert knowledge. The differences between a growing organism and a growing crystal are many and various, but it must suffice here to specify the simplest and most familiar sort of difference; and as it is convenient to take a possibly controversial statement of this kind from the writings of a physiologist, I quote here a passage from an article by Professor Fraser Harris, of Halifax, Nova Scotia, in the current number of the quarterly magazine called Science Progress edited by Sir Ronald Ross—
"Living animal bioplasm has the power of growing, that is of assimilating matter in most cases chemically quite unlike that of its own constitution. Now this is a remarkable power, not in the least degree shared by non-living matter. Its very familiarity has blinded us to its uniqueness as a chemical phenomenon. The mere fact that a man eating beef, bird, fish, lobster, sugar, fat, and innumerable other things can transform these into human bioplasm, something chemically very different even from that of them which most resembles human tissue, is one of the most extraordinary facts in animal physiology. A crystal growing in a solution is not only not analogous to this process, it is in the sharpest possible contrast with it. The crystal grows only in the sense that it increases in bulk by accretions to its exterior, and only does that by being immersed in a solution of the same material as its own substance. It takes up to itself only material which is already similar to itself; this is not assimilation, it is merely incorporation.
"The term 'growth,' strictly speaking, can be applied only to metabolism in the immature or convalescent organism. The healthy adult is not 'growing' in this sense; when of constant weight he is adding neither to his stature nor his girth, and yet he is assimilating as truly as ever he did. Put more technically: in the adult of stationary weight, anabolism is quantitatively equal to katabolism, whereas in the truly growing organism anabolism is prevailing over katabolism; and reversely in the wasting of an organism or in senile decay, katabolism is prevailing over anabolism. The crystal in its solution offers no analogies with the adult or the senile states—but these are of the very essence of the life of an organism....
"The fact, of course familiar to every beginner in biology, is that the crystal is only incorporating and not excreting anything, whereas the living matter is always excreting as well as assimilating. This one-sided metabolism—if it can be dignified with that term—is indeed characteristic of the crystal, but it is at no time characteristic of the living organism. The organism, whether truly growing or only in metabolic equilibrium, is constantly taking up material to replace effete material, is replenishing because it has previously displenished itself or cast off material. The resemblance between a so-called 'growing' crystal and a growing organism is verily of the most superficial kind."
And Professor Fraser Harris concludes his article thus:—
"Between the living and the non-living there is a great gulf fixed, and no efforts of ours, however heroic, have as yet bridged it over."
Note C.—Old Age
We know that as vitality diminishes the bodily deterioration called old age sets in, and that a certain amount of deterioration results in death; but it turns out, on systematic inquiry, that old age and death are not essential to living organisms. They represent the deterioration and wearing out of working parts, so that the vivifying principle is hampered in its manifestation and cannot achieve results which with a younger and healthier machine were possible; but the parts which wear out are not the essential bearers of the vivifying principle; they are accreted or supplementary portions appropriate to developed individual earth life, and it does not appear improbable that the progress of discovery may at least postpone the deterioration that we call old age, for a much longer time than at present. Emphasis on this distinction between germ cell and body cell, usually associated with Weismann, seems to have been formulated before him by Herdman of Liverpool.
Biologists teach us that the phenomenon of old age is not evident in the case of the unicellular organisms which reproduce by fission. The cell can be killed, but it need neither grow old nor die. Death appears to be a prerogative of the higher organisms. But even among these Professor Weismann adopts and defends the view that "death is not a primary necessity, but that it has been secondarily acquired by adaptation." The cell is not inherently limited in its number of cell-generations. The low unicellular organism is potentially immortal; the higher multicellular form, with well-differentiated organs, contains the germ of death within its soma. Death seems to supervene by reason of its utility to the species: continued life of an individual after a certain stage being comparatively useless. From the point of view of the race the soma or main body is "a secondary appendage of the real bearer of life—the reproductive cells." The somatic cells probably lost their immortal qualities on this immortality becoming useless to the species. Their mortality may have been a mere consequence of their differentiation. "Natural death was not introduced from absolute intrinsic necessity, inherent in the nature of living matter," says Weismann, "but on grounds of utility; that is from necessities which sprang up, not from the general conditions of life, but from those special conditions which dominate the life of multicellular organisms."
It is not the germ cell itself, but the bodily accretion or appendage, which is abandoned by life, and which accordingly dies and decays.
Footnotes
[32] See Explanatory Note A at end of chapter.
[33] See Explanatory Note B.