Page:Popular Science Monthly Volume 35.djvu/401

Rh It thus appears that the brain has a twofold connection with the muscular machinery of the body; that it not only supplies the stimulus required for the production of voluntary movements, necessitating a corresponding activity on its own part, but that it is stimulated in turn by the active muscles; since every contraction is a separate occasion for the return of responsive impulses to the brain, by means of which the corresponding centers there are informed of the degree of energy put forth, and the extent of the resulting movement. Voluntary movements are thus associated with three distinct kinds of consciousness: 1. That which accompanies the outgoing impulse from the brain—the so-called "sensation of innervation." 2. That excited by contraction of muscles through impulses arising within the muscle itself and thence transmitted to the brain—the true muscular sensation in which the muscle acts the part of a special sense-organ. 3. That produced by the resulting movement, also due to impulses sent to the brain—perhaps from the surfaces of the bones as they move against each other at the joints, or from the stretched and compressed tissues, especially the tendons in which many "Pacinian corpuscles" are found.

The brain is thus infused with a knowledge of the work done by the muscles, and hence of the external world of matter upon which the body acts by means of its muscles. These muscular tuitions—so-called intuitions—become permanent constituents of the mental life; and my third thesis is to the effect that the muscles play a rôle in the development of mind similar to that which belongs to the other special sense-organs—the eye, the ear, etc.

The dependence of intellect upon sensation was recognized by Aristotle in his famous dictum, "Nothing in the intellect not first in the senses"; and whatever the differences of view which divide the schools of psychology or individual psychologists as to the origin of our ideas of matter, time, and space, and whatever the real nature of the so-called "muscle-sense," all agree that the special sense-organs are the chief avenues of approach to the