Anger and fear express opposite emotional states. Fear is the expression of a strong desire to escape from danger; anger, of a strong desire to attack physically and to vanquish opposition. This hypothesis is strongly supported by the outward expressions of fear and of anger. When the business man is conducting a struggle for existence against his rivals, and when the contest is at its height, he may clench his fists, pound the table, perhaps show his teeth, and exhibit every expression of physical combat. Fixing the jaw and showing the teeth in anger merely emphasize the remarkable tenacity of phylogeny. Although the development of the wonderful efficiency of the hands has led to a modification of the once powerful canines of our progenitors, the ancestral use of the teeth for attack and defense is attested in the display of anger. In all stations of life differences of opinion may lead to argument and argument to physical combats, even to the point of killing. The physical violence of the savage and of the brute still lies surprisingly near the surface (Fig. 21). We have now presented some of the reasons based largely on gross animal behavior why fear is to be regarded as a response to phylogenetic association with physical danger. In further support of this hypothesis, I shall now present some clinical and experimental evidence. Although there is not convincing proof, yet there is evidence that the effect of the stimulus of fear upon the body when unaccompanied by physical activity is more injurious than is an actual physical contest which results in fatigue without gross physical injury. It is well known that the soldier who, while under fire, waits in vain for orders to charge, suffers more than the soldier who flings himself into the fray; and that a wild animal endeavoring to avoid capture suffers less than one cowering in captivity. An unexpressed smouldering emotion is measurably relieved by action. It is probable that the various energizing substances needed in physical combat, such as the secretions of the thyroid, the adrenals (Cannon), etc., may cause physical injury to the body when they are not consumed by action (Fig. 22).