brain, heart, and muscles of the face—before the passion is communicated to the other organism. All the acts of expression are, we think, best explained by this physiological and sociological law of solidarity and sympathy.
According to Darwin's theory of explanation, our expressional movements are habits, which, useful at first for the maintenance or defense of life, are preserved and transmitted after they no longer have immediate utility. Most of our gestures are of this class. The signs of affirmation and negation appear to have come from the infant's inclining its head to receive nourishment from its mother's breast, and turning it away when it does not want food. The same gestures, applied to all affirmation and negation, have become hereditary and instinctive with many nations. The acts of clinching the fists and displaying the teeth were primarily voluntary, as preparations for combat and signs of defiance of the enemy; they then became associated with the feeling of anger, then transmitted by heredity, till now we clinch our fist when the enemy is not present, and express the sneer of contempt by an exhibition of the teeth, joined with a backward motion of the head, but with no thought of biting.
However extended the effects of heredity may really be, we have a right to reproach Darwin for having given too great a part to the external causes, to selection and the medium. It is in the very tissues of the organism, in the inmost properties of the living substance, that we should first seek for the mechanical and physiological reasons for the phenomena of expression. Thus, the contraction of the eyebrows in struggle and in pain, which is explained by Darwin as a survival of a movement originally advantageous in combat, is shown by M. Mosso to be a result of the flow of blood to supply the waste of nervous force, and to be physiologically connected with movements of attention and of effort.
In the physiological view, the law that links the emotion with its exterior signs is the same that governs all the manifestations of life and force; it is the law of the equivalence of movements. At any particular moment, the quantity of nervous force corresponding to the state of consciousness called sensation has to expend itself in some way, and engender somewhere an equivalent manifestation of force. The expended force may itself follow three different courses. Sometimes the nervous excitation is transformed simply into cerebral movements corresponding with a mental agitation. This is what takes place, for example, when a child hears a story that interests and moves it. At other times the nervous excitation is transformed into movements of the viscera, and follows the ganglionic nerves. Agreeable thoughts, for example, aid digestion. Fear may paralyze the nerves of the intestine. The heart beats more rapidly under emotion, and sometimes stops, and this influence is accomplished through the means of the pneumogastric nerves. Or the nervous excitation, following the
