IX THE SKIN 195 



whether light affects the chromatophores directly or through 

 the central nervous system has received considerable atten- 

 tion. The latter alternative was espoused by Lister, who 

 found that a blinded frog no longer changes its color in 

 response to changes in the intensity of light. Lister's con- 

 clusion has been only partially confirmed by subsequent 

 investigators. Steinach found that if both the nerves and 

 blood vessels supplying any portion of the skin were cut in 

 two, there still remained in that part a certain capacity for 

 color change in response to light of different intensities. 

 When pieces of dark paper were laid over portions of the skin 

 thus treated, or even upon portions of skin entirely removed 

 from the body, the areas covered were found to be consid- 

 erably darker than those exposed to the light. Specimens 

 of Hyla in which certain parts were shaded while other parts 

 were exposed to light became light colored in all except the 

 shaded areas. This was found to occur both in normal frogs 

 and in frogs whose spinal cord was destroyed. Color changes 

 were found by Dutartre to take place more rapidly in normal 

 frogs than in specimens which had been blinded, but the 

 same reactions occurred in both cases. There is no doubt, 

 therefore, that light brings about color changes both directly 

 and through the central nervous system. 



The influence of the nervous system upon the chromato- 

 phores is shown by the experiments of several investigators. 

 Destruction of the optic thalamus causes the skin to become 

 much darkened (Steiner, Biedermann). Stimulation of the 

 medulla causes the skin to assume a lighter color. The skin 

 of the leg may be made to turn pale through stimulation of 

 the sciatic nerve. Biedermann has shown that color changes 

 may be brought about both through the spinal nerves and 

 the sympathetic system. If the spinal nerves supplying the 

 leg be cut, the skin of the leg may still respond to changes in 



