CUTANEOUS AND INTERNAL SENSATIONS. 



261 



carefully by von Frey.* To determine the location of the pressure 

 points he used fine hairs of different diameters fastened to a wooden 

 handle. The cross-areas of these hairs are determined by measure- 

 ments under the microscope, and the pressure exerted by each is 

 measured by pressing it upon the scale pan of a balance. The 

 quotient of the pressure exerted divided by the cross-area of the 



hair in square millimeters, - 2 , reduces the pressure to a uniform 



Fig. 112. 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. 



unit of area. For the pain points fine needles may be employed 

 or stiff hairs similar to those used for the pressure points. From 

 the experiments made there seems to be no doubt that each of 

 the four cutaneous senses has its own spots of distribution in the 

 skin, those for pain being most numerous and those for warmth 

 the least numerous. There is some reason for believing also that 

 the nerve endings mediating the pain sense lie most superficially 

 in the skin and those for the warm sense the deepest. 



* Von Frey, " Konigl. Sachsischen Gesellschaft der Wissenchaften. Math.- 

 phys. Klasse," 1894-95-96. 



