THE SKIN 391 



A sensation of cold will be perceived. This is 

 due to chemical irritation of the cold spots. The 

 temperature of the area does not fall. 



Electrical Stimulation. It has heen found that 

 the stimulation of a well-defined cold or warm 

 spot with moderately strong induced currents 

 causes a sensation of cold or warmth respectively. 



Temperature After-Sensation. Stimulate a cold 

 spot mechanically with a pencil point. Remove 

 the point. 



The sensation of cold outlasts the stimulus. 



Balance between Loss and Gain of Heat. Pro- 

 vide three beakers of water. Heat them to 20, 

 30, and 40 C., respectively. Place a finger of 

 one hand in the water at 20, and a finger of the 

 other hand in the water at 40. After the re- 

 spective sensations of cold and warmth have 

 disappeared, place both the fingers in the water 

 at 30. 



The finger from the cold water will seem warm 

 and that from the warm water cold. The tem- 

 perature of the skin equals the balance between 

 its heat loss and heat gain. When this tempera- 

 ture is raised or lowered, the warm spots or cold 

 spots respectively are stimulated. 



Fatigue. Provide three beakers containing 

 water at 10, 32, and 45 C. respectively. Place 

 a finger of one hand in the beaker at 32, and a 



