Cutaneous or skin sensation may arise from either _mechanical_ stimulation, such as pressure, a blow, or tickling, from _thermal_ stimulation from hot or cold objects, from _electrical_ stimulation, or from the action of certain _chemicals_, such as acids and the like. Stimulated mechanically, the skin gives us but two sensation qualities, _pressure_ and _pain_. Many of the qualities which we commonly ascribe to the skin sensations are really a complex of cutaneous and muscular sensations. _Contact_ is light pressure. _Hardness_ and _softness_ depend on the intensity of the pressure. _Roughness_ and _smoothness_ arise from interrupted and continuous pressure, respectively, and require movement over the rough or smooth surface. _Touch_ depends on pressure accompanied by the muscular sensations involved in the movements connected with the act. Pain is clearly a different sensation from pressure; but any of the cutaneous or muscular sensations may, by excessive stimulation, be made to pass over into pain. All parts of the skin are sensitive to pressure and pain; but certain parts, like the finger tips, and the tip of the tongue, are more highly sensitive than others. The skin varies also in its sensitivity to _heat_ and _cold_. If we take a hot or a very cold pencil point and pass it rather lightly and slowly over the skin, it is easy to discover certain spots from which a sensation of warmth or of cold flashes out. In this way it is possible to locate the end-organs of temperature very accurately. [Illustration: FIG. 17.--Diagram showing distribution of hot and cold spots on the back of the hand. C, cold spots; H, hot spots.] THE KINAESTHETIC SENSES.--The muscles, tendons, and joints also give rise to perfectly definite sensations, but they have not been named as have the sensations from most of the other end-organs. _Weight_ is the most clearly marked of these sensations. It is through the sensations connected with movements of muscles, tendons, and joints that we come to judge _form_, _size_, and _distance_. THE ORGANIC SENSES.--Finally, to the sensations mentioned so far must be added those which come from the internal organs of the body. From the alimentary canal we get the sensations of _hunger_, _thirst_, and _nausea_; from the heart, lungs, and organs of sex come numerous well-defined but unnamed sensations which play an important part in making up the feeling-tone of our daily lives.