Page:Physiological Researches upon Life and Death.djvu/41

Rh foundations for our judgment of external forms. Now let us suppose one half of the body to be differently disposed from the other, the same uncertainty in perception would be the result.

We conclude from what has been said, that in the whole apparatus of the external sensitive system, the harmony of action of two symmetrical organs, or of the two similar divisions of the same organ, is an essential condition to the perfection of sensation.

The external senses are the natural exciters of the brain, the functions of which, in animal life, constantly succeed theirs, and which would languish in perpetual inaction, did it not meet with, in them, the principle of its activity. Sensations are immediately derived from perception, memory, and imagination, and from these the judgment. Now it is easy to prove that these different functions, commonly designated by the term of internal senses, are governed by the same law in their exercise as the external senses, and that like these they advance so much the nearer to perfection, as there is more harmony between the two symmetrical portions of the organ in which they hold their seat.

Let us suppose, for example, one of the hemispheres to be more strongly organized and better developed at all points than the other, and therefore susceptible of being more vigorously affected; then, I say, the perception will be confused; for the brain is to the mind, what the senses are to the brain; it transmits to the mind the shock received from the senses, in like manner as these last communicate to it the impressions made upon them by surrounding bodies. Now if a defect of harmony in the external sensitive system can disturb the perceptions of the brain, why should not the mind perceive confusedly when the two hemispheres, unequal in point of force, do not combine in one, the double impression which they receive?