292 ALFKED C. REDFIELD 



1 . Coordinative action of the circulation 



a. Influence of the respiratory function of the circulation upon 

 melanophores. The circulation of the blood is obviously impor- 

 tant in maintaining the metabolic activity of the melanophores. 

 Stoppage of the circulation might be expected to produce effects 

 upon the state of the melanophores, either on account of failure 

 in the oxygen supply which must result or because of the accumu- 

 lation of carbon dioxide or other katabolic products in the tissues. 

 This expectation is readily realized. 



If a ligature is tied tightly about the leg of a horned toad, the 

 melanophore pigment of which is expanded, no immediate result 

 follows. In the course of two hours the skin of the ligatured leg 

 becomes very much paler than that of the rest of the body (fig. 

 7). Evidently the stoppage of circulation has caused a con- 

 traction of the pigment. Upon removing the ligature the circu- 

 lation is restored, and after an hour and a half the melanophore 

 pigment becomes expanded once more so that the color of the 

 leg is indistinguishable from the other parts of the skin. 



If small bits of skin containing expanded melanophore pigment 

 are cut from a horned toad and placed in a normal salt solution, 

 this pigment becomes contracted very rapidly, usually within 

 five or ten minutes. The skin of the horned toad also becomes 

 pale within a short time after the death of the animal. 



The contraction of the melanophore pigment in these cases 

 seems to be due to the interruption of the circulation. Whether 

 the reaction is due to a deficiency of oxygen or to an accumulation 

 of carbon dioxide or other waste materials in the tissue has not 

 been determined. The effect of anemia upon the melanophores 

 probably is not a thing which comes into play in producing any of 

 the usual melanophore reactions. Consequently, the other mode 

 of action of the circulation upon these cells will prove of greater 

 interest. 



b. The coordination of melanophores by hormones. The circu- 

 lation of the blood is known to influence the tissues to which it 

 flows by carrying to them chemical substances, such as hor- 

 mones, which excite the tissues to various forms of activity. In 



