TEMPERATURE SENSES IN FROG's SKIN 87 



is increased. Frogs which Torelle ('03) placed in water of 10°C. 

 immediately swam down and remained below, usually with legs 

 stiffly outstretched. In 1918 Brooks corroborated this by a 

 series of detailed observations on frogs which were placed in 

 water of decreasing temperature. As the water was cooled the 

 frogs remained for a shorter and shorter time at the surface till 

 at 5°C. they settled to the bottom and remained there. 



The skin is sensitive to variations in the temperature of air, of 

 water, and of acid solutions. Comparing the sensibilitj'' of the 

 skin and afferent nerves bj'^ treatment with warm and cool acid 

 solutions, Tarchanow ('72) was the first to point out that the 

 thermal end-organs must be in the skin and that the quicker 

 response to the warmer acid solutions was due to an increased 

 irritabihty in the nerve endings, agreeing in this with Archangel- 

 sky ('73) who had used the same stimulus. This sensitiveness 

 of the skin has been mentioned or investigated by recent workers 

 in connection with studies of other sense organs, and Koranyi 

 ('93) and Pearse ('10) found the frog's integument responsive 

 to both light and heat. Pearse secured responses from frogs 

 whose feet were dipped in water at 40°C. and 45''C. and Reese 

 ('06) obtained similar results from Cryptobranchus, while Parker 

 ('03) and Yerkes ('06) both alluded to the susceptibihty of the 

 skin to changes of temperature. 



Warmth produces a positive and cold a negative response to light. 

 When frogs were placed in warm air or water they moved toward 

 the light, but in the same media at 8°C. they moved away from 

 the light (Torelle, '03). L. J. Cole ('07) secured sunilar results 

 when he placed a frog in a dark box between a large and a small 

 illuminated area at the opposite ends. When the frog was cooled 

 to 6°C. and 10°C. it would move toward the smaller area, but 

 when warmed it would immediately move toward the larger one. 

 In order to compare the relative effects of light and heat, Pearse 

 ('10) arranged a series of tubes, with a measured heat radiation 

 upon the sides of a totally dark box. Another box contained a 

 light whose heat output was one-half that of the pipes. Eyeless 

 toads placed in these boxes proved to be almost totally indifferent 

 to the heat, but were strongh' phototropic, showing that light 



