Page:Popular Science Monthly Volume 12.djvu/759

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mind—excites, through the spinal cord, the various muscles, producing movement; but this condition is not absolutely necessary, since in decapitated animals, for instance, the nervous system of the spinal cord can of itself produce motion of the muscles. Here we have motor activity, but no sensibility. Sensibility exists only where the mind is intact and capable of perceiving, so that a creature which has no mind is void of sensibility. This fact is confirmed by pathological observation; for, whenever the mind is affected, there appear at the same time symptoms of disordered sensibility, and vice versa. And when we find a patient exhibiting notable disorder of the sensibility, then, if the nerves are intact, we can safely conclude that the central nervous system is affected, and to that degree that the mind has not escaped.

Anatomy and physiology here are in accord with pathology. Some animals possess little or no sensibility: they belong to the lower grades of animals; their intelligence is obscure, and their sensibility is as obtuse as their intelligence. On the other hand, if we consider animals of higher intelligence, we find their sensibility becoming more and more keen, till we come to man, at once the most intelligent and the most sensitive of animals. And even in man himself we find race differences, those races being most sensitive which possess the highest decree of intelligence. The anatomical structure of the nervous centres is in harmony with this coincidence, for it is in man that the posterior columns of the spinal cord are most voluminous, as compared with the anterior. Now, the anterior columns transmit the motor excitations to the nerves, while the posterior columns transmit the sensory excitations. Again, the posterior lobes of the brain in man, as compared with animals, are more developed than the anterior. But it is in the posterior lobes that perception of sensitive excitations appears to reside.

Nor is it surprising that there should exist so intimate a relation between mind and sensibility. Indeed, whatever may be the influence of the spontaneous development of the mind itself, resulting from the constitution of the brain, which is its organ, it still holds true that all our knowledge comes from our sensations, and from the brain-work thence resulting. Mind is, so to speak, the product of these two factors; and our notions of the world around us, elaborated and fecundated by the mind's spontaneous action, constitute individual personality. Hence, inasmuch as anatomy, physiology, and pathology, show intimate relation between sensibility and intelligence, we can justly say that psychology confirms the positive data furnished by these three sciences.

Accordingly, poisons which affect the intelligence are ipso facto poisons of the sensibility. In this respect alcohol does not differ from chloroform. When alcoholic intoxication is only beginning, we find already a notable degree of insensibility; but at the comatose stage