TEMPERATURE SENSES IN FROG's SKIN 111 



DISCUSSION AND RESULTS 



A temperature sense is easily demonstrable in the frog's skin. 

 There is a response to heat characteristic in iorm and reaction 

 time. The lowest degrees of heat which stimulate the skin lie 

 somewhere between 35°C. and 41°C. If the skin be stimulated 

 by water increasing in heat by 5°C. at each stimulation from 

 30°C. to 50°C., the first response may be expected at 35°C. If 

 the same series is followed except that the heat be increased by 

 1°, the first response may occur at 40°C. or 41°C. The skin 

 responds to the higher degrees of heat with great regularity. 

 As the heat is increased from 35°C. to 50°C. the reaction time 

 decreases with more or less regularity from long intervals (25, 

 15, 12 seconds) to short ones (2, 1 second). 



It will be remembered that some of the early workers main- 

 tained (Goltz, '69; Heinzmann, '72) that if reflex frogs were 

 stimulated gradually enough with increasing heat they could 

 be subjected to considerable warming without resistance. My 

 investigations show only a slight agreement with them which has 

 been mentioned. It has not been possible to stimulate the foot with 

 increasing heat beyond 43°C. without response, even when the 

 frog's foot was suspended in a beaker of water at 20°C. and the 

 heat almost imperceptibly increased by an inflow of warm water. 

 The long reaction time of the heat response agrees with v. Frey's 

 contention that the heat receptors are in the deeper and the 

 cold receptors in the more superficial layers of the skin. 



It has been possible to isolate the temperature sense from the 

 tactile and chemical. This has been done by treatments with 

 1 per cent solution of cocaine. Crozier ('16) used this method in 

 separating the tactile and chemical senses, and by it Cole ('10) 

 eliminated response to pain, but preserved sensitiveness to taste. 

 The separation of temperature from other senses gave the follow- 

 ing results. Response to acid (0.5 per cent hydrochloric) per- 

 sisted beyond response to heat. Pain persisted beyond heat; 

 heat and cold beyond touch. With the thermal and chemical 

 stimulations care has been taken to immerse the same amount 

 of surface. It has of course not been possible to make any 



