EXPRESSION. Our mental states, and particularly our emotions, are closely linked with certain muscular and physiological asso ciates, which are exhibited in perhaps the great est detail and variety by the muscles and blood vessels of the face. These associates are de nominated expressions; they include not only the visible muscular and vascular phenomena which have already been indicated, but also a vast number of more or less obscure respiratory, circ-ulatory and secretory changes. These changes and movements are at times strilcing in their apparent inutility, so that much labor has been spent in the effort to elucidate their reason for being. The first explanation of the expressions which possess much interest at the present day is that of Darwin. In accordance with his evolutionism, he regards many emo tional expressions as rudirnents of actions which have been useful to the animal either in its individual history or in the history of the race. An acquired example of this sort is the point ing of the pointer dog. Other expressions are held to be the result of tendencies opposing those which would be called into play by the opposing emotion. A dog approaching its master playfully will evince in its relaxed muscles, in its bent back, in its flexed limbs, in its wagging tail and ears laid badc, actions exactly the opposite of the tense sinews, the straight back and forward pointed head, the rigid extended limbs, the uplifted tail and ears which betoken its desire to attack another dog and serve to frighten its antagonist or to facili tate its attack. The third factor in the produc tion of emotional expression, according to Darwin, is the direct overflow of the rxcited nervous system into motor channels, as in the case of trembling from fear.
Wundt retains Darwin's third principle of expression, but replaces the other two by the principle of association, which causes an ex perience to assume the physical correlates of related experience, and the principle of the connection of movement with sense-ideas, which includes all cases of movements which indicate or symbolise the object of the emotion or its desired result. The facial expression of dis like is an example of the former of these prin ciples; it represents an attempt to eliminate a bitter-tasting substance from those parts of the mouth where it will be tasted most. Exemples of the second principle are the stare of surprise or the clenching of the fist in anger.
James retains Darwin's first principle that many expressions are rudimentary purposeful actions, and Darwin's third principle of nervous overflow. He adds to these what is equivalent
to Wundt's principle of the association of analogous sensations, and two new explana tions of expression. The first of these is that not only are formerly useful emotional expressions retained as rudiments, but that their physiological consequences and concomitants undergo a like atrophy and schematisation. Be sides all these, there is a class of reactions sus ceptible to no very simple explanation. These have been perpetuated in a more or less mechanical manner, independently of their mode of origin. Perhaps the greater number of facial expressions belong to this class.
In accordance with the James-Lange theory of the emotions, which holds that they are con stituted by their expressions, James maintains that there are distinct and different expressions of every emotion. This has been denied by Cannon, who has made perhaps the most thorough physiological investigation into the actual nature of emotional expression. He finds that all intense emotions are characterized by the increased secretion of adrenalin and the liberation of the carbohydrates stored in the liver. These reactions are directly serviceable to the individual in whom they happen (1) be cause they cause the blood to be driven from the abdominal viscera to the muscles, heart, brain and lungs, where it is more needed in any sudden action; (2) because they release an im mediately available store of energy; (3) because they cause the heart to act more vigorously and more rapidly.; (4) because they increase the clotting power of the blood and decrease Immorrhage in case of injury. The milder emotions, on the other hand, are characterized by a directly antithetical physiological process, in which the normal action of the digestive system and other abdominal vicera is helped rather than hindered. The milder emotions are associated with a preponderant activity of the cerebro-spinal nervous system, while the violent ones belong rather to the sympathetic system. See Eucrriox.
Bibliography.— Cannon, W. B., 'Bodily Change in Pain, Hunger, Fear and Rage' (New York 1915) ; Darwin, (The Expression of the Emotions in Man and Animals' (London 1873) ; James, W., (Principles of Psychology' (New York 1890) ; Mantegazza, P., (Physiognomy and Expression) (3d ed., London 1904) ; Warner, F., (Physical Expression> (New York 1886) ; Wundt, (Grundziige der Physiologischen Psy chologie) (Leipzig 1911) ; (Volkerpsy.chologie) (Leipzig 1900).