280 



THE SPECIAL SENSES. 



The Punctiform Distribution of the Cutaneous Senses. 

 A most interesting fact 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 



. 



Fig. 119. Representation of the distribution of cold and warm spots on the volar 

 surface of forearm in a space 2 cms. by 4 cms. The red dots represent the cold spots as 

 tested at a temperature of 10 C. The black dots represent the warm spots as tested at a 

 temperature of 41 to 48 C. 



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, 

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

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



