The pigmentary effector system. I.—Reaction of frog's melanophores to pituitary extracts

The ability of certain organisms, including notably the Mollusca and lower Vertebrata, to respond to their surroundings by appropriate pigmentary changes has long been familiar to biologists; it has been recognised for more than half a century that a special type of effector organs (chromatophores, melanophores, etc.) are actively instrumental in producing such changes, and that, in Vertebrates at least, pigmentary response is partially controlled through the nerves by stimuli received from the organs of vision. During the past two decades it has been shown that the reactions of the pigment cells to stimuli simulate those of other effector organs, especially as regards their responses to certain internal secretions. That a fuller understanding of their properties might prove of service to practical aspects of physiology, as well as the key to a knowledge of “colour adaptation,” was realised by Lister, who concludes his paper on the cutaneous pigmentary system of the Frog (1858) with the following comment: “The pigmentary system also promises to render good service in toxicological enquiry. Hitherto in experiments performed on animals with that object attention has been directed chiefly, if not exclusively, to the effects produced upon the actions of the nervous centres, the nerves, and muscles. In the pigment cells we have a form of tissue with entirely new functions, which, though apparently allied to the most recondite processes, yet produce very obvious effects… Such experiments are so readily performed, and the effects produced are so obviously indicated by the changes in colour of the integument, that I venture to recommend this method of investigation to those who are occupied in studying the action of poisons. …” A considerable literature, which has been reviewed too thoroughly and recently to merit an extensive epitome here, bears witness to the intricacy of the mechanism which underlies pigmental response in Fishes, Amphibia, and Reptiles; and very little work has been done on Molluscs in this connection. It can be safely asserted that as many distinct types of chromatophores are already known as there are different sorts of other effector organs whose properties have been studied. Hence it is obvious that, apart from the intrinsic interest presented by the phenomenon of colour change, a study of the properties of this series of effectors invites consideration in relation to a fuller understanding of therôle played respectively by the character of tissue and the nature of its nerve supply in the local action of drugs. The research, of which this preliminary communication contains an initial account, of the response of Amphibian melanophores to pituitary extracts, has been approached with both these objectives in view. For present purposes it will suffice to recapitulate briefly what has already been achieved in relation to the endocrine factors in pigmental response.