394 ANDREW JOHNSON BIGNEY 



and the concentration of adrenin was strong enough to be poison- 

 ous to the animals. It is, therefore, not surprising that he failed 

 to observe the real action of the drug. Furthermore, since the 

 adrenin and light act in the same way, the real action of the drug 

 could not be noticed in the light condition. Had Klett carried 

 on his tests with frogs kept in the dark instead of the light, I 

 am convinced that his results would have agreed with Fujita's 

 and mine. 



To determine the concentration necessary to produce the mi- 

 gration of the retinal pigment, frogs that had been kept in the 

 dark were injected with adrenin in strengths varying from one 

 part in a thousand to one in one hundred million. The frogs 

 were subjected to the influence of the drug for one hour and then 

 killed. At concentration one to one thousand there was com- 

 plete expansion of the pigment, at one to ten thousand almost 

 complete, at one to fifty thousand there was less expansion and 

 less regularity in the condition of the preparation, and at one to 

 one million or one to five million the results were not very uni- 

 form. While the influence of the adrenin could still be detected 

 at these dilutions, there was an irregularity which recalled the 

 variation often noticed in normal frogs. The action of the 

 drug on the retinal pigment is possible in even greater dilutions. 

 This sensitiveness of the retina is in marked contrast with that 

 of the skin, which is not nearly so responsive. There seems to 

 be no sharp ending in its influence either on the skin or the re- 

 tina, but a gradual diminution. 



To determine how long the influence of the adrenin on the 

 retinal pigment lasted, a number of frogs kept in the dark were 

 injected with a solution of adrenin one in one thousand and the 

 eyes were prepared at hour intervals from one to six. After 

 an hour the pigment showed complete expansion; after two hours 

 somewhat reduced expansion; in three to four hours still further 

 reduction, and in five to six hours the retraction was complete, 

 thus showing that the influence passes off in about four hours. 



It is clear from these experiments that adrenin causes a con- 

 traction of the pigment in the dermal melanophores and an ex- 

 pansion of that in the retinal cells — processes precisely the oppo- 

 site of each other. 



