In defining health much depends on the point of view. The average man considers, himself healthy when he is not ill, and many persons who is suffering ill, on endemic disease, e.g. Malaria or hookworm, considers himself well, just because he is not seriously sick. The physiologist would consider health as a normal functioning of the cell, because he takes as the unit of his investigation. The sociologist and Psychologist on the other hand, looks upon the body from the point of view of action, and he must describe health in terms of the whole man as he reacts upon the various stimuli which come either from within or from without. These reactions are, however, ultimately medicated in the brain or in the mind, and they will be the most perfect and economical the less friction there is in the physical organism.