Page:Popular Science Monthly Volume 7.djvu/673

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HAT is instinct? What is its relation to intelligence? These questions form the subject of my lecture to-day.

Many persons would probably object to this subject being treated at all in a course of physiology. Many persons doubtless think that these are questions for the psychologist, and not for the physiologist. But I think you have already perceived, in the course of these lectures, how difficult, yea, impossible, it is to sharply separate these two departments. As between all other departments of science, so also between these, there is a border-land, which is common ground. The physiology of the brain is that common ground.

The precise relation of physiology to psychology it is extremely difficult to adjust. As there are two opposite errors in regard to vital force—one, the old error of regarding this force as something innate, underived, unrelated to other forces of Nature; the other, the new error of regarding it as nothing but ordinary physical and chemical forces, and thus identifying physiology with chemistry and physics—so also on this subject there are two opposite errors: one the old error of regarding mental forces as wholly unrelated to and underived from vital forces, and psychology, as wholly disconnected from physiology; the other, the new error of regarding mental phenomena as connected with the brain in the same clear and intelligible way that functions are connected with organs, and thus identifying psychology with physiology. But, as in the case of vital force, there is a truer view, viz., that which regards this force as indeed correlated with other lower forces and derived from them, but, nevertheless, as a very distinct form of force or cosmic energy, producing a very distinct and peculiar group of phenomena, the knowledge of which constitutes the science of physiology; so also, on the subject of mental force, there is a truer view which comprehends and embraces the extremes mentioned above.

Let me briefly explain my views on this subject. In recent times physiology has indeed made great, and to many startling, advances in the direction of connecting mental phenomena with brain-changes. Physiologists have established the correlation of physical and chemical with vital forces, and probably of vital with mental forces. They have proved in every act of perception the existence of a vibratory thrill passing along the nerve-cord from sense-organ to brain; and in every act of volition a similar vibratory thrill from brain to muscle; they have even determined the velocity of this vibratory thrill, and find it, to the surprise of those who identify nervous force with