5. There are certain other emotional states associated with energy and the energy feeling of great interest. What we call eagerness, enthusiasm, passion, refers to the intensity of an instinct, wish, desire or purpose. In childhood this energy is quite striking; it is one of the great charms of childhood and is a trait all adults envy. For it is the disappearance of passion, eagerness and enthusiasm that is the tragedy of old age and which really constitutes getting old. Youth anticipates with eagerness and relishes with keen satisfaction. The enthusiasm of typical youth is easily aroused and sweeps it on to action, a feature called impulsiveness. Sympathy, pity, hope, sex feeling--all the self-feelings and all the other feelings--are at once more lively and more demonstrative in youth, and thus it is that in youth the reform spirit is at its height and recedes as time goes on. What we call "experience" chills enthusiasm and passion, but though hope deferred and a realization of the complexity of human affairs has a moderating, inhibiting result, there is as much or more importance to be attached to bodily changes. If you could attach to the old man's experience and knowledge the body of youth, with its fresher arteries, more resilient muscles and joints, its exuberant glands and fresh bodily juices,--desire, passion, enthusiasm would return. In the chemistry of life, passion and enthusiasm arise; sickness, fatigue, experience and time are their antagonists. This is not to deny that these energy manifestations can be aroused from the outside. That is the purpose of teaching and preaching; the purpose of writer and orator. There is a social spread of enthusiasm that is the most marked feature of crowds and assemblies, and this eagerness makes a unit of thousands of diverse personalities. Further, the problem of awakening enthusiasm and desire is the therapeutic problem of the physician and especially in the condition described as anhedonia. In anhedonia, as first described by Ribot, mentioned by James, and which has recently been worked up by myself as a group of symptoms in mental and nervous disease, as well as in life in general, there is a characteristic lack of enthusiasm in anticipation and realization, a lack of appetite and desire, a lack of satisfaction. Nothing appeals, and the values drop out of existence. The victims of anhedonia at first pass from one "pleasure" to another, hoping each will please and satisfy, but it does not. Food, drink, work, play, sex, music, art,--all have lost their savor. Restless, introspective, with a feeling of unreality gripping at his heart, the patient finds himself confronting a world that has lost meaning because it has lost enthusiasm in desire and satisfaction.