TEMPERATURE SENSES IN FROG S SKIN 



105 



one was the same extension of the toes, and stretching of the web 

 accompanied in some frogs by a spasmodic upward jerk of the 

 leg as soon as the tip (table 14) of the toe touched the water 

 (no. 23, exp. 2, table 15). Two frogs had persistently long 

 reaction periods of two and eight seconds, but a very short 

 interval was typical of the cold response. 



After a dependable cold response had been shown to occur, 

 further steps were necessary to prove that the cold receptors 



TABLE 14 



Response of foot to water at 2°C. Feet normal. Reaction allowance, 30 seconds. 



Stimulation period, 2 minutes 



were in the skin. Their location in its superficial layers had 

 already been suggested by the short reaction interval. In experi- 

 ments recorded in table 15 responses to cold were invariably 

 eliminated by a half-hour cocaine treatment, whereas this only 

 retarded the heat reaction. The records of the alternate stimu- 

 lation of the normal foot and the cocained foot by water at 2°C. 

 showed a clock-like regularity in the response of the normal foot. 

 At what temperature does the skin become responsive? A 

 definite beginning point (39° to 43°) has already been established 

 for the heat response, but investigations of the cold limitations 

 have not yet been mentioned. 



