CUTANEOUS AND INTERNAL SENSATIONS. 281 



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 or tactile sense and the pain sense 

 are also distributed in a punctiform manner; they have been 

 studied most carefully by von Frey.* To determine the loca- 

 tion of the pressure points he used fine hairs of different diam- 

 eters fastened to a wooden handle. The cross-areas of these 

 hairs are determined by measurements under the micro- 

 scope, 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 

 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. 



Specific Nerve Energies of the Cutaneous Nerves. Many 

 attempts have been made to determine whether the doctrine of 

 specific nerve energies applies to these cutaneous senses; that is, 

 whether each sense has its own nerve fibers capable of giving only its 

 own quality of sensation. The evidence, on the whole, is favorable 

 to this view. According to some observers, electrical or mechanical 

 stimulation of the different points calls forth for each its character- 

 istic reaction. Donaldson has found that cocain applied to the 

 eye or throat destroys the senses of pain and pressure, but leaves 

 those of heat and cold, which again supports the view of separate 

 fibers for each sense. In addition there are a number of interesting 



