The Pigmentary Effector System, 



327 



suggested by the possibility of an antidromic control. The subsequent 

 action of pituitary extract was tested at varying intervals following doses 

 of different magnitude, to make certain both as regards time of action and 

 amount of drug administered, that the full effect of the latter would be 

 exerted. In no case did the normal response fail to make its appearance. 

 The indications are therefore that the pituitary melauophore stimulant acts 

 directly on the melanophores of the frog and not on the nerve-endings, as is, 

 indeed, fully consonant with what is at present known of the mode of action 

 of the other pituitary autocoids. 



Neither curare, atropine nor cocaine affect the melanophores of the frog 

 in any way. While injection evoked its maximum effect in decerebrated 

 frogs which had received just over the normal dose of curare adequate to 

 produce general motor paralysis, it should be noted that very large doses of 

 curare did prevent the melanophore response to pituitary injection before the 

 circulation had actually ceased. Eepeated tests, with a wide range of doses, 

 showed that atropine does not cause the melanophores of the frog to expand 

 as do those of the fish Ftmclidus when so treated (Spaeth). Laurens (1915) 

 has also noted the inefficacy of atropine to induce expansion in the con- 

 tracted melanophores of the Axolotl. The different mode of reaction of the 

 dermal melanophores of Fishes and Amphibia towards both atropine and the 

 pituitary autocoid would suggest that the term " dermal melanophore " has 

 been applied to more than one type of effector organ. It is intended to 

 reserve, for fuller discussion at a later stage, the reactions of frog melano- 

 phores to drugs ; but it may here be mentioned, in connection with the 

 antagonism of atropine and pilocarpine in respectively paralysing and 

 stimulating parasympathetic and secretory nerve-endings, that the latter 

 re-agent does not induce expansion of the contracted melanophores in the frog. 

 Were these structures innervated by the parasympathetic it would be 

 expected that either one or the other would operate in this way. Apocodeine 

 which, as Dixon (1904) has shown, effects general sympathetic paralysis, 

 brings about a darkening of the skin, not sufficient, however, to mask the 

 subsequent effect of pituitary administration. This is fully consonant with 

 the reaction of the melanophores to adrenalin, and the direct evidence given 

 by Hooker (1912) in regard to the relation of sympathetic stimulation to 

 melanophore contraction. 



Finally, the reaction studied in the experiments here recorded, leads to the 

 possibility that the nervous system may not be such an all-important factor 

 in the mechanism of " colour adaptation " as it has been customary to believe 

 in the past. Laurens (1915) concludes from his experiments on the pigment 

 responses of blinded and seeing axolotls, that in " colour adaptation " among 



