MOVEMENTS IN THE VISUAL CELLS 167 



suiting increase of catabolic products causing the cone myoid 

 to shorten." Although Dittler's statement is not altogether 

 clear, it seems evident that low temperature was supposed not 

 only to reduce the metabohsm of the retina to a low level, 

 but also to render the cone myoid less 'empfindhch' to chemical 

 stimulation. 



The conditions in the dark-adapted cones of fishes, however, 

 are entirely different, for here not only do the cone myoids 

 elongate when the temperature is increased, but also elongated 

 cones can be made to shorten by the use of low temperatures. 

 If the shortening of the cones of fishes in the fight were due to 

 a chemical stimulation, how can the elongation of these elements 

 in the dark through the action of heat be explained, since mani- 

 festly in this case the metabolic equilibrium tends to become 

 destroyed, the result being the formation of an excess of catabolic 

 wastes, which by analogy with the conditions in the frog, should 

 cause the cone myoids to shorten? Moreover, the efficiency 

 of low temperature in retracting elongated cones, and the cor- 

 relation between the uniform degree of myoid elongation and 

 the temperature gradient (p. 155) finds no explanation through 

 Dittler's hypothesis. 



It should be said, however, that Dittler strictly limited his 

 conclusions, the experimental evidence for which appears to 

 be well established, to the material upon which he worked, and 

 was even reserved in suggesting the occurrence of a similar 

 method of stimulation in living animals. 



The reason why the rods of Ameiurus move in darkness, while 

 the cones do not, may be as follows. The rod myoid normally 

 shortens in the dark, whereas the cone myoid elongates. It is 

 probable that the contractile function of the mj'oid is more 

 vigorous than the reverse process of elongation. This is not 

 only substantiated by the fact that dark adaption of the rod 

 takes less time than light adaption, but also by experiments 



'* Dittler did not formulate this conception in extenso as I have expressed it. 

 yet several statements (pp. 317-318) show that this was his belief. A concluding 

 quotation reads: .... "der Einfluss der Temperatur uberhaupt ganz nach 

 physikalischen Modus zu Wirken scheint, und bereciitigt uns, seine Wirkung rein 

 in diesem Sinne zu fasscn." 



