have an historic value for us, in the proof that this great philosopher recognized two things in the brain: first, a physiological mechanism; and then, above and beyond that, the thinking faculty of the soul. These ideas are nearly the same with those that afterward prevailed among many philosophers and some naturalists; the brain, in which the most important functions of the nervous system are performed, was for them not the real organ of thought, but simply the substratum of intelligence. Indeed, the objection was often enough expressed, that the brain forms a physiological exception to all the other organs of the body, in that it is the seat of metaphysical manifestations, which the physiologist has no concern with. It was perceived how digestion, respiration, movement, etc., could be referred to the phenomena of mechanism, of physics, and chemistry; but it was not allowed that thought, intelligence, and will, could be subjected to like explanation. There is, it was said, a chasm between the organ and the function, because the question is about metaphysical phenomena, and not at all about physico-chemical mechanism. De Blainville, in his lectures on zoology, laid great stress on the distinction between the organ and the substratum. "In the organ," he said, "there is a visible and necessary connection between anatomical structure and function; in the heart, the organ of circulation, the form and arrangement of valves and orifices account perfectly for the circulation of the blood. In the substratum, nothing like this is observable; the brain is the substratum of thought; thought has its seat in the brain, but it cannot be inferred from the brain's anatomy." Such considerations served as a foundation for the belief that, in cases of insanity, the reason might be affected essentially, as it was termed; that is, without the existence of any lesion in the substance of the brain. Even the converse was asserted, and cases are cited in physiological treatises of the unimpaired manifestation of intelligence in persons with softened or indurated brains. The progress of modern science has destroyed all such doctrines; yet it must be admitted that those physiologists who have drawn from the most delicate recent researches into the structure of the brain the conclusion that thought must be localized in a particular substance, or in nerve-cells of a determinate form and order, have equally failed to solve the problem, since they have done nothing more, in reality, than to oppose materialistic theories to other spiritualistic theories.
From what has been said, I shall draw the only conclusion which legitimately results; namely, that the mechanism of thought is unknown to us—a conclusion with which every one will probably agree. None the less the fundamental question I have suggested exists; for what concerns us is to know whether our present ignorance on this subject is a relative ignorance which will vanish with the progress of science, or an absolute ignorance in the sense of its relating to a vital problem which must forever remain beyond the ken of physiology. For myself, I reject the latter opinion, because I deny that scientific truth can thus