MELANOPHORES OF THE HORNED TOAD 297 



ment of the frog. Stockard ('15) and Spaeth ('16a) report the 

 same to be true of the melanophores of Fundulus. 



If a dilute solution of adrenin^ in isotonic sodium chloride solu- 

 tion is injected under the skin of a horned toad, a complete con- 

 traction of the pigment ensues; the dark bands across the back 

 and legs stand out boldly against the ground-color, which becomes 

 bright cinnamon-buff (fig. 12). This condition is produced by 

 injections of 0.2 cc. of a solution of adrenin diluted to one part in 

 100,000 and occasionally by a solution of one part in 1,000,000. 

 Weaker solutions, 1 : 10,000,000 and occasionally 1 : 100,000,000, 

 produce a contraction of the melanophore pigment over a more 

 circumscribed area, centering about the point at which the solu- 

 tion is introduced (fig. 11). The latter effect is especially inter- 

 esting because it is a close duplication of the condition produced 

 by injecting blood from an excited horned toad into an unexcited 

 individual. A comparison of figures 10 and 11 will make this 

 point obvious. 



It may be concluded from these facts that adrenin produces an 

 effect upon the melanophores of the horned toad identical with the 

 action of the hormone which appears in the circulation of these 

 lizards during nervous excitement.^ 



The adrenal glands of the horned toad consists of two elon- 

 gated, yellow bodies situated in the membranes which support 



^ 'Adrenalin-chloride' of a concentration of 1 : 1000 in physiological salt solu- 

 tion prepared by Parke-Davis and Company has been employed as a starting- 

 point in making up the solutions used throughout these experiments. 



' Gudernatsch ('14) has reported that tadpoles of Rana temporaria "fed on 

 (horse) adrenal cortex become much lighter than those fed on adrenal medulla or 

 any other food." 



This observation suggests that some secretion of the cortical part of the 

 adrenal gland may be the melanophore hormone, instead of adrenin itself. This 

 hypothesis was investigated in the following way. Extracts of the cortex and 

 of the medulla of fresh beef adrebals were made. It was found that both extracts 

 produced a contraction of the melanophores of Fundulus heteroclitus and of the 

 horned toad. The extract of the medulla ivas effective at much greater dilutions than 

 that of the cortex. Upon examining these extracts chemically it was found that 

 both contained adrenin, but the extract of the medulla contained a much greater 

 quantity than did the cortical extract. It seems justifiable, therefore, to conclude 

 that adrenin is the substance concerned in the contraction of the melanophores, 

 and not some constituent of the cortical part of the adrenal gland. 



