166 LESLIE B. AREY 



anaesthesia. As will be shown, carbon dioxide and other anaes- 

 thetics do, in fact, arrest the movements of all the retinal elements 

 of fishes. 



Dittler ('07) accounted differently for the absences of elonga- 

 tion in the cones of isolated frog's retinas which were introduced 

 from light into darkness. In order to appreciate his way of 

 viewing this situation, it is necessary to understand the general 

 theory advanced by him to explain the movements of the cones. 

 In darkness an equilibrium was supposed to exist in the metab- 

 olism of the retina, the elongated cone myoid representing an 

 unstimulated condition. Through the action of light, however, 

 catabolic processes preponderate, and the accumulated acid 

 wastes chemically stimulate the myoid to shorten. These con- 

 clusions were based upon experimental evidence by which it 

 was shown that weak, free acids could be detected if isolated 

 retinas were subjected to light in Hmited amounts of Ringer's 

 solution, and further that such an acid solution was capable of 

 causing other dark-adapted cones to shorten while still in the. 

 dark. To return to the case under consideration, Dittler believed 

 that the accumulation of the catabolic products formed in the 

 light merely continued its contractile influence after the isolated 

 retina was removed into the dark, and since these products were 

 not removed, the metabolic equiUbrium could never be restored 

 and consequently elongation failed to occur. 



This theory of chemical stimulation is not supported by the 

 condition in Fundulus and especially in Abramis, where the 

 cones of excised eyes do not shorten even when exposed to light, 

 for under these favorable conditions the tendency toward the 

 production of a catabolic excess should be maximum. In still 

 another way Dittler's theory does not explain a typical response 

 of the cones of fishes. The cone myoid in isolated retinas of 

 the frog shortens when the temperature is raised to 30°C. or 

 more in the dark (fig. 36), and this fact Dittler used to sup- 

 port his view in the following logical manner. It is well known 

 that most chemical reactions are accelerated by raising the 

 temperature; hence in this case the autonomic equilibrium 

 normally existing in the dark would become disturbed, the re- 



