MOVEMENTS IN THE VISUAL CELLS 133 



B. EFFECT OF TEMPERATURE (NORMAL ANIMALS) 



a. Retinal -pigment 



No investigations have hitherto been made to determine the 

 effect of temperature on the retinal pigment of fishes, whereas 

 several workers have used the frog for experimentation of this 

 kind. The problem considered here was to determine the re- 

 sponse of the retinal pigment of normal fishes and amphibians to 

 various temperatures, both in light and in darkness. 



/. Fishes. Experiments in the light were performed in tlie 

 following way. Light-adapted" fish were placed in large battery 

 jars close to north windows where they received strong diffuse 

 daylight; sheets of white paper were always placed under the 

 jars to aid reflection.^ The highest temperature to which 

 it is safe to subject fishes is about 28°C., although by gradual 

 elevation a somewhat higher temperature can be withstood 

 (Loeb and Wasteneys, '12). A low temperature that did not 

 vary beyond the limits of 3° and 5°C. was produced l)y intro- 

 ducing small pieces of ice directly into jars with the fish. At this 

 temperature fish are for the most part inactive, the respiration 

 rate decreases and they remain quietly at the bottom of the jars. 



At the end of an experiment, which was never less than threes 

 hours long, the eyes were excised and immersed in fixing fluid 

 in the light. ^ 



During the earliest trials retinas from the same fisli were 

 compared, eyes being subjected to the extreme temperatures in 



* The terms 'light adaption' and 'dark adaption' as used throughout tliis paper 

 imply that the animals had been previously subjected for a inininmm of 4 hours 

 either to bright diffuse daylight or to total darkness. 



' The possibility of a dark background influencing the (listril)ution of retinal 

 pigment was considered. Such a visual control, if present, would correspond 

 to the known role of the eye, as determined bj' Pouchet ('76) and others, in ani- 

 mals which adapt their bod)- color to the immediate environment. A series of 

 careful comparisons, however, failed to show any recognizable differences be- 

 tween the pigment distribution in the retinas of fishes that had been kept over 

 dark or light backgrounds. 



* In all work which involved the use of temperature, the fixing fluid was kept 

 at the same temperature as that at which the experiment had been performed. 

 Such treatment eliminated a possible source of slight error. 



