260 THE SPECIAL SENSES. 



a deep or subcutaneous sensibility to pressure and movements, 

 a sensibility which must be mediated through sensory fibers 

 contained in the nerves to the muscles. In the skin itself there 

 are present two kinds of sensory fibers. One variety conveys 

 sensations of pain and of extreme changes in temperature, but 

 the sensations are imperfectly localized. This kind of sensation 

 is found in the viscera also, and it may be considered from the 

 functional standpoint as a defensive agency toward pathological 

 changes in the tissues; it is designated as protopathic sensibility. 

 The second group of fibers responds to stimulations by light 

 pressures and small differences in temperature. These fibers 

 regenerate after lesions much more slowly than the protopathic 

 variety, and since the sensations mediated by them are localized 

 very exactly they furnish us the means for making fine discrim- 

 inations of touch and temperature. For this reason they are 

 described as an epicritic system and the corresponding sensations 

 are designated as epicritic sensibility. This system of fibers is 

 not found in the other organs, and it constitutes, therefore, the 

 special characteristic of the skin area. 



The Punctiform Distribution of the Cutaneous Senses. 

 A most interesting feet in regard to the cutaneous senses is that 

 they are not distributed uniformly over the whole skin, but are 

 present in discrete points or spots. This fact was first clearly 

 established by Blix,* although it was discovered independently 

 by Goldscheider and in this country by Donaldson. These ob- 

 servers paid attention chiefly to the warm and cold spots. The 

 existence of these spots may be demonstrated easily by anyone 

 upon himself by moving a metallic point gently over the skin. 

 If the point has a temperature below that of the skin it will be 

 noticed that at certain spots it arouses simply a feeling of contact 

 or pressure, while at other spots it gives a distinct . sensation of 

 coldness. If, on the other hand, the point is warmer than the 

 skin it will at certain spots give a sensation of warmth. On mark- 

 ing the cold and warm spots thus obtained it is found that they 

 occupy different positions on the skin. Elaborate charts have 

 been made of the warm and cold spots on different regions 

 of the skin, the apparatus usually employed being a metal 

 tube through which water of any desired temperature may be 

 circulated. The temperature of the skin, whatever it may be, 

 forms the zero line; any object of a higher temperature stimulates 

 only the warm spots, while one of a lower temperature acts upon 

 the cold spots. The pressure sense and the pain sense are also 

 distributed in a punctiform manner; they have been studied most 



* Blix, "Zeitschrift f. Biologic," 20, 141, 1884; Donaldson, "Mind," 39 

 1, 1885. See also Goldscheider, "Archiv f. Physiologic," 1885, suppl. volume 



