MELANOPHORES OF THE HORNED TOAD 287 



nozzle could not form a disturbing factor. After three minutes the right 

 side was much paler than the left; after six minutes the melanophore 

 pigment of the right side was completely contracted. The left side 

 remained unchanged until the nozzle was applied to it, when it, too, 

 became pale. 



This experiment, repeated on a number of animals, indicated 

 that if a portion of the skin of a horned toad is heated while in the 

 dark, the expanded melanophore pigment of that portion will 

 contract much more rapidly than that of the other parts of the 

 body. That this result is not produced by the contact of the 

 apparatus, but is a true temperature effect, is shown by the 

 fact that the application of the nozzle to the skin of a horned toad 

 does not produce a more rapid contraction of the melanophore 

 pigment of that part of the skin if the water within the nozzle is at 

 room temperature. 



The converse experiment, the application of a low temperature 

 to a small part of the skin, is illustrated in the following protocols: 



December 18, 1913. A nozzle through which ice water was running 

 was applied to the side of a horned toad the melanophore pigment of 

 which was contracted. Throughout thirty minutes of this treatment, 

 during which the animal was kept in the dark, no change occurred in the 

 condition of the pigment cells. 



In the same way a low temperature (10.5°C.) was applied to the side 

 of a horned toad of which the melanophore pigment was expanded. 

 The animal w^as in the dark. After six minutes the melanophore pig- 

 ment of the animal had contracted, as might be expected in the dark. 

 The melanophore pigment of the chilled portion of the skin did not con- 

 tract in twice that time. 



From these experiments it appears that the local application of 

 low temperatures to the skin of the horned toad cannot call forth 

 an expansion of the melanophore pigment,^ but that an expansion 

 previously established may be maintained in the region of low 

 temperature, though the rest of the skin becomes pale. 



^ The action of a low temperature when applied locally to the melanophores is 

 discordant with the results of applying light and heat and excluding light locally. 

 It may be pointed out that the facts are no more readily explained by the assump- 

 tion that nerves are concerned in the reaction, so that the point does not argue 

 for or against the ability of the melanophores to respond directly to the stimula- 

 tion of light and temperature. 



