Page:Philosophical Review Volume 1.djvu/500

484 central network, so that stimulus may traverse the whole system. The central connections may be so traversed as to produce an exceedingly complicated series of outward movements, as in the feats of somnambulists, or the still more wonderful performances of hypnotic subjects, without any trace being left in the memory of the conscious subject, and probably without any accompaniment of consciousness at the time of the action. It is even conceivable, so large is the provision for automatism in the nervous system of man, that a person might live for months, or even years, in a perfectly unconscious condition, the bodily organism answering periodically to the sense-stimulations entering and producing movements along the pre-established lines of least resistance ordained by previous habit, and causing such actions as those of eating, drinking, turning, rising, and perhaps even those of walking. These considerations have led certain writers to regard consciousness as an "epi-phenomenon," a kind of appendix to the book of life added to the completed volume, a sort of afterthought suggested too late for insertion in the text. Perhaps, however, we might find a deeper truth in the allegory if we should say that consciousness is a generously devised epitome in which the great argument of the book is briefly summarized.

If only some neural changes are attended with consciousness, it is necessary to ask under what conditions it arises. Richet, in his Psychologie Generale, enumerates the following physiological conditions of consciousness: (1) Circulation of the blood. The cessation or interruption of the circulation isfollowed by a syncope of consciousness. A moment's pressure of the great arteries supplying blood to the brain renders the subject unconscious. (2) Respiration. The psychic effects of asphyxia are well known. At the end of the first minute, there is an increasing distress. At the end of the second minute, an intense pain supervenes with suffocation accompanied by convulsive and epileptiform movements. In the midst of this