Page:The Source and Aim of Human Progress.djvu/15



BOUT twenty-five years ago I published in my Psychology of Suggestion a series of experiments on Normal and Abnormal Suggestibility, carried on at various laboratories including my own laboratory. I developed the psycho-physiological theory of the subconscious, traced the causation and nature of subconscious activities, and worked out the laws of normal and abnormal suggestibility. The following pertains to our present subject:

The nervous centers of man's nervous system, if classified as to function, may be divided into inferior and superior. The inferior centers are characterized by reflex and automatic activities. A stimulus excites the peripheral nerve-endings of some sense-organ. At once a nerve-current is set up in the afferent nerves. The current in its turn stimulates a plexus of central ganglia, the nerve energy of which is set free, and is propagated along the efferent nerves towards muscles and glands,—secretions, muscular contractions and relaxations are the result; biologically regarded, various reactions and adjustments follow.

Ingoing and outgoing nerve currents with their various end-reactions may be modified by the nerve centers. Nerve currents may be intensified, decreased in energy, or even entirely inhibited by central ganglia or by their mutual interaction and interferences. Sherrington and other physiologists have by a number of experiments formulated some of the important principles of such physiological activities. The law of inhibition or interference early formulated by Ziehen may suffice: "If an excitation of a definite intensity (m) take place in one cortical element (b), and another excitation of a different intensity (n) take place at the same time in another cortical element (c) which is connected by a path of conduction with element (b), the two intensities of excitation may modify each other."

Although such modifications frequently occur, it nevertheless remains true that the inferior nerve-centers are of a reflex nature.