440 THE SPECIAL SENSES 



portion of the skin and to locate on such a map by different 

 colored dots the position of the different sources of sen- 

 sation. The relation of these spots to the fibers may be 

 summarized as follows: (a) The surface of the skin is di- 

 vided into spots or areas in the center of which is the end- 

 ing of a sensory fiber. (&) Each of the four cutaneous 

 senses has its own areas and fibers, and stimulation of one 

 of these spots produces only one kind of sensation, heat or 

 cold, warmth or pressure, (c) The pain spots are most 

 numerous and the warmth spots least numerous. The 

 ends of the pain fibers are nearest the surface and those 

 of the warmth fibers farthest below the surface, {d) Dis- 

 crimination between two stimuli of the same kind depends 

 upon the stimulation of two distinct fibers. Thus, we 

 feel the pressure of two points as two only when each 

 point stimulates a different pressure fiber from the other, 

 (e) Fibers of a given kind are much nearer together in certain 

 parts of the skin than in others, and sensitiveness in any 

 given direction depends partly upon the nearness together 

 of the fibers. 



Pressure. — The pressure spots are, next to the pain spots, 

 the most numerous. In those portions of the body which 

 are covered with hair the pressure fibers terminate in a 

 ring surrounding the hair follicle. These rings, therefore, 

 form the end organs. In other parts of the body the tactile 

 corpuscles seem to function as end organs. These cor- 

 puscles are particularly abundant on the tips of the fingers 

 where they underlie the dermal papilla^. It is estimated 

 that on the entire body exclusive of the head region there 

 are about five million pressure spots. These spots are 

 very close together on the tips of the fingers and less near 

 in other parts of the body. 



