But another school of psychology, of which the late Prof. William James is a leading authority, holds that the physical expression precedes and causes the mental state. For instance, in the cases above cited, the perception of the anger-causing or fear-causing sight first causes a reflex action upon the muscles, according to inherited race habits of expression. This muscular expression and activity, in turn, is held to react upon the mind and to cause the feeling or emotion of anger or fear, as the case may be. Professor James, in some of his works, makes a forcible argument in support of this theory, and his opinions have influenced the scientific thought of the day upon this subject. Others, however, have sought to combat his theory by equally forcible argument, and the subject is still under lively and spirited discussion in psychological circles. Without taking sides in the above controversy, many psychologists proceed upon the hypothesis that there is a mutual action and reaction between emotional mental states and the appropriate physical expression thereof, each in a measure being the cause of the other, and each likewise being the effect of the other. For instance, in the cases above cited, the perception of the anger-producing or fear-producing sight causes, almost or quite simultaneously, the emotional mental state of anger or fear, as the case may be, and the physical expression thereof. Then rapidly ensues a series of mental and physical reactions. The mental state acts upon the physical expression and intensifies it. The physical expression in turn reacts upon the mental state and induces a more intense degree of the emotional feeling. And so on, until the mental state and physical expression reach their highest point and then begin to subside from exhaustion of energy. This middle-ground conception meets all the requirements of the facts, and is probably more nearly correct than either extreme theory. Darwin in his classic work, "The Expression of the Emotions in Man and Animals," has thrown a great light on the subject of the expression of emotion in physical motions. The Florentine scientist, Paolo Mantegazza, added to Darwin's work with ideas of his own and countless examples drawn from his own experience and observation. The work of François Delsarte, the founder of the school of expression which bears his name, is also a most valuable addition to the thought on this subject. The subject of the relation and reaction between emotional feeling and physical expression is a most fascinating one, and one in which we may expect interesting and valuable discoveries during the next twenty years.