172 LESLIE B. AREY 



The effect of certain drugs, as quinine and strychnine, upon 

 the retinal pigment ('protoplasmagifte') is in dispute. It is 

 clear, however, from the work of Ovio ('95) and of Lodato ('95) 

 that cocaine can arrest pigment migration. 



As a precaution against a possible source of error, animals 

 were never introduced from one condition of light or darkness 

 to the other without having been previously subjected to a 

 brief preliminary treatment of the anaesthetic which was to be 

 tested. 



a. Retinal pigment 



1. Carbon dioxide. The carbon dioxide used in these experi- 

 ments was a commercial soda-water product sold under the trade 

 name of Tureoxia.' Quantitative determinations of the con- 

 centrations used were made by titration with fo sodium 

 carbonate, using phenolphthalein as an indicator. 



In the first experiments made on Ameiurus the movement of 

 the pigment was arrested by a strong solution of carbon dioxide, 

 but since none of the animals survived such treatment the 

 obvious objection exists that the pigment cells also may have 

 been killed. 



A slight refinement in method consisted of revivifying the 

 fishes at intervals, by temporary removal to running water, 

 until opercular movements were restored. By this method 

 fishes were kept alive for 2 hours, during which time four or 

 five revivifying treatments were necessary. The migration of 

 retinal pigment was shown to be checked both in light and in 

 darkness, yet controls proved that the cells were not permanently 

 injured. 



A method which gave more satisfactory results was devised 

 after repeated trials had given a mixture of tap water and car- 

 bonated water of sufficient strength to anaesthetize an Ameiurus 

 but not to prohibit opercular movements of greatly reduced 

 amplitude. The record of an experiment will well illustrate 

 both the method and the results. 



Experiment 4-i-6- A dark-adapted Ameiurus was placed in a 

 mixture of 1 part of Tureoxia' to 4 parts of tap water, and after re- 



