For over thirty years I have been interested in the varying symptomatology of disease of the same kind occurring in different individuals. The subject of pain naturally received most attention. In this paper I shall take up mainly individual sensitiveness to pain, substitution symptoms, and radiations of pain. Some other important subjects, such as sensitiveness of diseased blood vessels and pains due to them, can only be touched on. Besides summarizing my earlier publications,1 I shall give a survey of recent investigations. Theoretical questions will not be discussed. Nor can the vast and remarkable general literature on pain be reviewed. Like all others, I am deeply indebted to the studies of Ross, Goldscheider, Head, Mackenzie, Hurst and many others. Many methods of gaging sensitiveness to pain have been suggested. The simple test that I employ is carried out by first pressing the thumb against the tip of the mastoid