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. It may be said that these are mere mechanical actions, and have nothing to do with the acts which we associate with intelligence.
But let us consider what takes place in such an act as reading aloud. In this case, the whole attention of the mind is bent upon the subject matter of the book, while a multitude of most delicate muscular actions are going on, of which the reader is not in the slightest degree aware. Thus the book is held in the hand, at the right distance from the eyes; the eyes are moved, from side to side, over the lines, and up and down the pages. Further, the most delicately adjusted and rapid movements of the muscles of the lips, tongue, and throat, of laryngeal and respiratory muscles, are involved in the production of speech. Perhaps the reader is standing up and accompanying the lecture with appropriate gestures. And yet every one of these muscular acts may be performed with utter unconsciousness, on his part, of anything but the sense of the words in the book. In other words, they are reflex acts.
The reflex actions proper to the spinal cord itself are natural and are involved in the structure of the cord and the properties of its constituents. By the help of the brain we may acquire an affinity of artificial reflex actions. That is to say, an action may require all our attention and all our volition for its first, or second, or third performance, but by frequent repetition it becomes, in a manner, part of our organization, and is performed without volition, or even consciousness.
