this formula is justified, it will be sufficient for our present purpose to select but one or two. "The stinging and contractile powers of a polyp's tentacle correspond to the sensitiveness and strength of the creatures serving it for prey. Unless that external change which brings one of these creatures in contact with the tentacle were quickly followed by those internal changes which result in the coiling and drawing up of the tentacle, the polyp would die of inanition. The fundamental processes of integration and disintegration within it would get out of correspondence with the agencies and processes without it; and the life would cease." So in higher animals, "every act of locomotion implies the expenditure of certain internal mechanical forces, adapted in amounts and directions to balance or out-balance certain external ones. The recognition of an object is impossible without a harmony between the changes constituting perception, and particular properties coexisting in the environment. Escape from enemies supposes motions within the organism, related in kind and rapidity to motions without it. Destruction of prey requires a particular combination of subjective actions, fitted in degree and succession to overcome a group of objective ones. And so with those countless automatic processes exemplified in works on animal instinct." And similarly, as will appear still more clearly when we come to treat especially of the evolution of intelligence, "the empirical generalization that guides the farmer in his rotation of crops, serves to bring his actions into concord with certain of the actions going on in plants and soil; and the rational deductions of the educated navigator who calculates his position at sea, constitute a series of mental acts by posed from a resultant into an initial condition, the name given to the whole group of phenomena becomes the personification of the phenomena, and the product is supposed to have been the producer. In lieu of regarding vital actions as the dynamical results of their statical conditions, the actions are personified, and the personification comes to be regarded as indicating something independent of and antecedent to the concrete facts it expresses.' Problems of Life and Mind, vol. i. p. 110.

which his proceedings are conformed to surrounding circumstances."

We practically recognize the truth of this definition of life when we attempt to ascertain whether an animal is dead or alive by poking it with a stick. If it responds by motions of its own, we judge it to be alive; if it merely moves as the stick pushes it, we judge it to be dead. So we decide whether a tree is alive or dead by observing whether the increased supply of solar radiance in spring causes those internal motions which result in the putting forth of leaves. these cases we recognize the truth "that the alteration wrought by some environing agency on an inanimate object does not tend to induce in it a secondary alteration, that anticipates some secondary alteration in the environment. But in every living body there is a tendency towards secondary alterations of this nature; and it is in their production that the correspondence consists."

This formula for vital phenomena is further illustrated and justified by the fact that the degree of life is low or high, according as the correspondence between internal and external relations is simple or complex, limited or extensive, partial or complete, imperfect or perfect. The lowest forms of life respond only to the simpler and more homogeneous changes which affect their total environment. The relations established within a plant answer only to the presence or absence of a certain quantity of light and heat, and to the chemical and hygrometric relations existing in the enveloping atmosphere and subjacent soil. In a polyp, besides general relations similar to these, certain more special relations are established in correspondence with the external existence of mechanical irritants; as when its tentacles contract on being touched. The increase of extension acquired by the correspondences as we ascend the animal scale, may be seen by contrasting the polyp, which can simply distinguish between soluble and insoluble matters,

or between opacity and translucence in its environment, with the keen-scented bloodhound, and the far-sighted vulture. And the increase of complexity may be appreciated by comparing the motions respectively gone through by the polyp on the one hand, and by the dog and vulture on the other, while securing and disposing of their prey. In the next chapter it will be shown that the advance from lower to higher forms of life consists in the orderly establishment of relations within the organism, answering to external relations of coexistence and sequence, that are continually more special, more remote in space and in time, and more heterogeneous; until at last we reach civilized man, whose intelligence responds to every variety of external stimulus, whose ordinary needs are supplied by implements of amazing complexity, and whose mental sequences may be determined by circumstances as remote as the Milky Way and as ancient as the birth of the Solar System.

When viewed under this aspect the phenomena of life and of intelligence are so similar that it is difficult to keep them separate in our series of illustrations. As we proceed to treat of psychology, we shall much better appreciate the importance of the truth which I am now expounding. Restricting ourselves here, as far as possible, to physiological illustrations, let us note that in any organism life continues just so long as relations in the environment are balanced by internal relations, and no longer. The difference in result between a jump from a horse-car and a jump from an express train running at full speed, depends simply on the difference in the ability of the contracting muscles to neutralize a small or a large quantity of arrested momentum. The motor energy with which the head is carried forward until it strikes the ground, is exactly the surplus of external force to which the organism has failed to oppose an internal force. If the resulting concussion of the brain is not so great as to induce instant death, but only causes inflamma

tion, with temporary loss of consciousness, then the continuance of life will depend upon the ability of the molecular forces within the organism to bring about a redistribution of matter and motion which shall balance the sudden redistribution caused by the blow. Dynamical pathology regards all diseases as disturbances of the internal equilibrium of the organism, and recovery is the restoration of the equilibrium. The avoidance of danger is the coordination of certain actions in anticipation of more or less complex relations about to arise without. If disease and danger be successfully avoided, the death which ensues in old age is due to the diminished plasticity of the organism which renders it incapable of responding to external changes. As we saw when treating of the primary aspects of Evolution and Dissolution, the evolution of the body, even to the close of life, is characterized by the integration of its constituent matter, shown in the increasing proportion of solids to fluids which makes the bones brittle, the muscles stiff, and the nerves sluggish. Death from old age ensues just when the consequent molecular immobility has reached the point at which incident forces can no longer be balanced by internal rearrangements.

A paragraph will suffice for the exposition of this formula of life in connection with the general law of evolution. That the evolution of life upon the earth, beginning with innumerable jelly-like patches of protoplasm, like the monera discovered by Prof. Haeckel, and ending with more than two million species of plants and animals such as naturalists classify, has been a change from homogeneity to heterogeneity, will be denied by no one. Nor is it needful to repeat, save for form's sake, what was sufficiently illustrated in an earlier chapter, that the higher forms are also those in which the various orders of integration are most completely exemplified. We need only to note that the continuous adjustment of the organism to its environment,

in which process we have seen that life consists, must necessitate both the differentiation of the organism and the integration or definite combination of the changes which constitute its activity. For as the life becomes higher the environment itself increases in heterogeneity as well as in extent. The environment of a fresh-water alga is, as Mr. Spencer remarks, limited to the ditch or pool in which the alga lives. The acaleph borne along on a wave of the sea has a much more homogeneous environment than the caterpillar which crawls over leaves; and the actions by which the caterpillar must "meet the varying effects of gravitation," are far more heterogeneous than the actions of the acaleph. In the case of the higher animals, not only is their environment extremely heterogeneous as consisting to a great extent of adjacent organisms which stand to them in the relations of enemies, competitors, or prey; but it also presents highly coordinated actions on the part of these organisms, which must be met by highly coordinated actions on the part of the former. Thus with the increase of the organism in heterogeneity, definiteness, and coherence, its environment increases in heterogeneity and presents more definite and coherent relations to which the organism must adjust itself. And in this way the heterogeneous, definite, and coherent activity of the organism is again enhanced. The corollary from this group of truths is one which will nearly concern us when we come to treat of the Evolution of Society it is this, the greater the amount of progress already made, the more rapidly must progress go on.