294 ALFRED C. REDFIELD 



From this experiment, which has been repeatedly confirmed, 

 it is apparent that by blocking the circulation to one leg of the 

 horned toad without interfering with the innervation of the leg 

 noxious stimuli are prevented from influencing the melanophores 

 of that leg. This result is to be expected if the melanophore pig- 

 ment is contracted by a hormone liberated in the circulation by 

 noxious stimuh. 



The fact that the melanophore pigment of the isolated leg 

 becomes contracted upon the removal of the ligature (fig. 9), sev- 

 eral minutes after the cessation of stimulation, confirms the hy- 

 pothesis further. 



If noxious stimuli cause the production of a hormone in the 

 blood which contracts the melanophore pigment, one might 

 expect that blood drawn from a horned toad which had been 

 thrown into a state of nervous excitement by this means would 

 cause the contraction of the pigment of an unexcited animal 

 when injected into its body. How far this expectation is realized 

 is indicated by the following account of such an experiment: 



July 28, 1915. 2.00 P.M. Needle of hypodermic syringe inserted 

 into the lymph space under the skin of the right side of a horned toad 

 the melanophore pigment of which was expanded fully. 



2.52 P.M. Through this needle was injected 0.5 cc. of defibrinated 

 blood drawn from the neck of a second horned toad, which had been 

 made very pale by stimulating the mouth with a weak faradic current for 

 ten minutes. 



3.04 P.M. The skin of the first horned toad has become clearly 

 pale along the right side of the hack (fig. 10). The melanophore pig- 

 ment of some lateral scales near the point of insertion of the needle has 

 contracted. 



3.18 P.M. No change. 



3.28 P.M. Pale patch is becoming darker. 



3.50 P.M. Pale patch is almost indistinguishable from the rest of 

 skin. 



7.00 P.M. Pale patch has entirely disappeared. 



This experiment indicates that the blood of an excited horned 

 toad will cause a contraction of the melanophore pigment of an 

 unexcited animal. The size and intensity of the pale area varied 

 considerably in different experiments. In no case did it extend 

 beyond the side of the body into which the blood was injected. 



