126 LESLIE B. AREY 



greatest care was not exorcised, the retina proper easily separated 

 from the pigmented epithelium. On the whole, the first method 

 was ])ref erred to the second because of the wrinkling of the retina 

 that usually accompanied the use of the latter. 



Sections were cut 7 ^u to 10 /x thick, and except in a few special 

 cases only those passing through the region of the optic nerve 

 were retained for examination. Preparations were stained with 

 Ehrlich-Biondi's triple stain or were double stained in Heiden- 

 hain's iron hematoxyhn and a plasma counterstain. Ehrlich- 

 Biondi in some instances gave excellent differentiation of all 

 elements, while at other times it would show the capriciousness 

 in producing satisfactory results for which it is notorious; iron 

 hematoxylin gave uniformly good preparations. 



It often became necessary to bleach the pigment in order to 

 study the visual cells, which would otherwise be masked by the 

 partially or completely extended processes. The method em- 

 ployed was essentially that of Mayer ('81), in which nascent 

 oxygen^ is the effective agent. 



The aim of the present investigation has been to determine 

 the influence of light, temperature, anaesthetics and oxygen 

 on the movements of the rods, cones, and retinal pigment in 

 the normal and excised eyes of fishes and of amphibians. 



To Prof. G. H. Parker, under whose direction this research 

 has been conducted, I wish to acknowledge my indebtedness for 

 much inspiration and valuable suggestion. Advantage is taken 

 of this opportunity to express appreciation for the facilities of 

 the Zoological Laboratory placed at my disposal by the Director, 

 Prof. E. L. Mark, and for many courtesies extended by him 

 during my residence at Cambridge. 



3. EXPERIMENTAL PART 

 A. DETERMINATION OF ADAPTION TIMES 



Before extensive experimentation can be undertaken on the 

 retinal elements, it is necessary to determine the various lengths 



3 When potassium chlorate and hydrochloric acid interact, it is commonly 

 said that nascent chlorine is the agent causing bleaching. As a matter of fact 

 the reaction liberates free oxygen. 



