certain functions have been delegated to particular groups of cells. Those of the nervous system have assumed and discharge the functions with which psychic phenomena are associated. As the single original row of nervous cells developed into a spinal cord, the psychic manifestations were handed over to that. As the spinal cord developed greater ganglia at one of its extremities, the more important of the psychic manifestations were passed on to these superior ganglia. Out of these developed the hind-brain, the mid-brain, the fore-brain, the total cerebrum in man, so that, as Goethe guessed, the skull is only the greatest of the vertebræ, and to the cellular contents of this crowning structure were at last transferred those neuroses which accompany human consciousness.
Consciousness is never strictly simple. Its very name implies the apprehension of at least two elements which are known together. The very essence of intellect is discrimination. But this proceeds to no great length without assimilation, that is, the apprehension of similarity. The whole fabric of knowledge consists in the sum of apprehended resemblances and differences. All thought is unification or differentiation. Its materials lie in the objects of consciousness. Its process consists in the consciousness of likeness and difference. Its laws are reducible to the principles of identity, contradiction and excluded middle. What we call “reason” is the unity which harmonizes diversity. Its categories are at once the forms of thoughts and of things, for otherwise thought and its objects would have no common bond and reason would know no necessity. Consciousness is this sense of unity. There may be sense-presentations without it, although the philosopher is not in a condition to experience them. A dog, a portion of whose cerebrum has been removed, may be excited by the presence of food; but he cannot co-ordinate his sense presentations. We may say that he is without consciousness. Consciousness is the string upon which the pearls of sense are strung. Break the string, and the pearls are scattered, but they do not cease to be. The string is broken when the co-ordinating centres in the brain are rendered inoperative by any cause. These centres
