TEMPERATURE SENSES IN FROG S SKIN 



95 



included in the table. At 40° C. the normal foot of each frog 

 responded after an average reaction time of 10 seconds. At 45°C. 

 the cocained foot responded after an average reaction interval 

 of 16.75 seconds against an average of 8 seconds for the normal 

 foot. Such results showed that when the skin was anaesthe- 

 tized the temperature sense was affected — a clear proof that the 

 heat receptor is located only in the skin. 



In order to test this question further, however, the cutaneous 

 nerve supply was cut off by severing the sciatic nerve at the thigh. 

 In four frogs thus treated the injured and the normal leg were 



TABLE 5 

 Responses in seconds to heat increasing by 5°C. at each stimulation in a range of 

 15°C. to 45°C. Right foot cocained 30 minutes. Left foot normal. Reaction 

 allowance, 30 seconds. Stimulation time, 2 minutes, m = no response 



alternately stimulated by the same degree of heat, but not the 

 shghtest response was obtained from the denervated leg, showing 

 that the response was in no sense purely muscular. From three 

 other frogs the skin of one foot was removed. The feet of one 

 were alternately immersed in water of increasing temperature, 

 those of the other two were dipped in water at 45°C. Again 

 there was no reaction except in the normal foot whose responses 

 were uniform with those already secured. Hence the skin of the 

 frog's foot is essential to these reactions. The results of these 

 experiments show that the temperature sense is at once affected 

 by cocaine, and that it is entirely eliminated by destruction of 

 the cutaneous nerve supply or by removal of the skin. 



