Biologically the skin senses are more important to the human being than is either sight or hearing. The blind man and the deaf man are merely handicapped, but a man totally without skin sensitivity would have a poor chance to survive at all. Pain guards the body from external injury. The temperature senses act as external thermostats in the vital task of regulating the temperature of the blood. Even touch, although less essential, provides a critical aid in darkness. Yet, compared with sight or hearing, the skin senses have attracted relatively little attention, and they remain a rich field for further investigation. There are three persistent problems of major interest, and most research techniques have been directed toward their solution. These problems concern the number of skin senses, the nature of the receptors and receptor processes, and the measurement of the actual manner of their stimulation.In connection with the number of skin senses, touch, pain, warm, and cold are commonly assumed to be the four basic ones, but this view has not been universally accepted. Many years ago Head [41] proposed two separate cutaneous systems, the epicritic and the protopathic, each having a separate set of four senses. Katz [30] suggested a separate vibration sense, independent of touch. At the other extreme, Nafe [35] would like to reduce warmth, cold, and some kinds of pain to sensations from dilating and constricting blood vessels, thus eliminating these as separate skin senses. The problem is further complicated by the presence of deep pain and deep pressure sensitivities, which are difficult to distinguish from the strictly cutaneous reactions.In regard to the nature of the receptors and the way in which they work, mapping the skin with small stimulators shows that there are points of high sensitivity-the warm, cold, pain, and touch spots-with