Every stage in this long process, every new attempt to place physical phenomena in a chain of direct causation has been denounced as dangerous and degrading materialism, and in this sense Huxley was not only an adherent but one of the foremost champions of materialism. As everyone knows, some of the greatest advances in this process of co-ordinating physical phenomena were made during Huxley's life; and his vigorous onslaughts on those who tried to thwart all attempts at material explanations in favour of unknown agencies made him specially open to abusive criticism. The battle was almost invariably between those who had not special knowledge and those in possession of it, and it occurred in practically the whole field of science, but particularly in the biological sciences. A single example will serve to shew what is meant by materialism in this sense and the attitude of Huxley to it. The study of the human mind naturally has attracted the attention of thinkers almost since the beginning of philosophy, but until this century, with a few crude exceptions, it has been conducted entirely apart from anatomy and physiology. Advances in these physical sciences, however, have changed that, and the modern psychologist has to begin by being a physiologist and anatomist. "Surely no one who is cognisant of the facts of the case, nowadays, doubts that the roots of psychology lie in the physiology of the nervous system. What we call the operations of the mind are the functions of the brain, and the materials of consciousness are products of cerebral activity. Cabanis may have made use of crude and misleading phraseology when he said that the brain secretes thought as the liver secretes bile; but the conception which that much-abused phrase embodies is, nevertheless, far more consistent with fact than the popular notion that the mind is a metaphysical entity seated in the head, but as independent of the brain as a telegraph operator is of his instrument. It is hardly necessary to point out that the doctrine just laid down is what is commonly called materialism. I am not sure that the adjective 'crass,' which appears to have a special charm for rhetorical sciolists, would not be applied to it. But it is, nevertheless, true that the doctrine contains nothing inconsistent with the purest idealism." The whole doctrine of evolution is similarly a materialistic account of natural phenomena, in the popular and not the philosophical meaning of the term. But even within this popular meaning, it is extremely necessary to have an exact conception of the limits within which Huxley was materialistic. Take for instance the question of the origin of life. It would be one of the greatest achievements of physical science could it shew that life was not inco-ordinate with non-living physical phenomena, but was a special case of them. Huxley knew that this advance had not yet been made.