434 LESLIE B. AREY 



KXPKIUMKNTATION 



Individuals of Hiina pipiens, ai)])r()xiinately uniform in size, 

 were exposed to ])right diffuse daylight for eight hours, or to 

 total darkness for a minimum length of twenty-eight hours. 

 At the expiration of these periods of light and dark-adaption, 

 the cranium of each animal was first split sagit tally, and then 

 cut transversely just caudad to the eyes. The resulting moieties 

 of the cranium, with the contained eyes, were dropped into 

 Perenyi's chromo-nitric fixative; in this solution they underwent 

 fixation, the condition of illumination being identical with that 

 to which they had been experimentally subjected. The oper- 

 ation on dark-adapted animals was accomplished by the light 

 from a photographic red lamp and demanded but a few seconds 

 time. 



After dehydration and the removal of the lens, the eyes were 

 imbedded in paraffine, sectioned 8m thick, and stained with 

 Ehrlich-Biondi's acid fuch^in-orange G-methyl green mixture. 

 In light-adapted retinas the expanded pigment masked the 

 visual cells to a greater or less degree, hence, nascent oxygen 

 was used as a bleaching agent in these preparations. The 

 results obtained with the Ehrlich-Biondi stain were very satis- 

 factory, yet it is of interest to note that the staining reaction of 

 several definite structures was often variable. For example, the 

 outer member of the red rod in most cases stained red with the 

 acid fuchsin, yet in some retinas from the same series they were 

 colored an intense orange from the orange G, although the treat- 

 ment in both cases had been, so far as is known, identical, the 

 series having been carried along simultaneously step by step. 

 Moreover, in one preparation, at least, it was observed that the 

 outer members in one half of the retina were stained orange, 

 whereas in the other half they were stained red. This selective 

 stainability is doubtless indicative of a variable physiological 

 cytoplasmic state. Preparations in which the outer members 

 of red rods selected the orange G, showed the green rods stained 

 red with the acid fuchsin. In retinas that had been bleached 

 (potassium chlorate and hydrochloric acid being the reagents 



