But what physical science does is not to discover the hereditary element, but to render it distinct -- to give us an accurate conception of what we may expect, and a good account of the evidence by which we are led to expect it. Let us see what that science teaches on the subject; and, as far as may be, I will give it in the words of those who have made it a professional study, both that I may be more sure to state it rightly and vividly, and because I would rather have it quite clear that I have not made my premises to suit my own conclusions.

First, then, as respects the individual, we learn as follows: Even while the cerebral hemispheres are entire, and in full possession of their powers, the brain gives rise to actions which are as completely reflex as those of the spinal cord.

When the eyelids wink at a flash of light, or a threatened blow, a reflex action takes place, in which the afferent nerves are the optic, the efferent, the facial. When a bad smell causes a grimace, there is a reflex action through the same motor nerve, while the olfactory nerves constitute the afferent channels. In these cases, therefore, reflex action must be effected through the brain, all the nerves involved being cerebral. When the whole body starts at a loud noise, the afferent auditory nerve gives rise to an impulse which passes to the medulla oblongata, and thence affects the great majority of the motor nerves of the body.