MOVEMENTS IN THE VISUAL CELLS 161 



by me, yet it seems improbable that such a small difference would 

 cause the cones to shorten maximally. Any error that could 

 be introduced during these determinations would tend to shorten 

 the cones, hence Herzog's results are at a disadvantage in this 

 respect. I have continued experiments for hours, yet the 

 results were always the same; in no case was there found a gen- 

 eral shortening of the cones that in any way resembled the ex- 

 treme condition at 33°C. 



From these results, which, in a general way, are the reverse 

 of those found in fishes, it is evident that the responses of the 

 cones are not comparable to those of the retinal pigment. The 

 pigment may indeed be under nervous control, so that stimulat- 

 ing agents such as heat, cold and light produce a migi-ation ac- 

 cording to the principle of specific energies, j-et if the cone cells 

 are influenced by the nervous system, these experiments can not 

 be said to furnish proof of such a relation. 



In order that there should be no doubt concerning the etlect 

 of low temperature upon the cone myoid, a further determina- 

 tion was made long after the results which are tabulated above 

 were obtained. In this later experiment rigorous precautions 

 were observed to eliminate possible errors. After frogs (R. 

 pipiens of various sizes), kept at a temperature of 18°C., had been 

 subjected to a ])reliminary treatment of darkness for 72 hours, 

 they were introduced into a vessel cooled to 1°C, where they 

 remained for a period of 4 hours. The eyes were then quickly 

 excised in dim, red light, the operation not requiring more than 

 15 seconds, after which they were returned into darkness where 

 fixation at approximately the freezing temperature ensued. 

 The average measurements of the cone myoids in these prepara- 

 tions were as follows: 12 to 14 m; 10 to 15.4 n; 10 to 14 m; 10 to 

 11 m; 13 to 15.4 n;9 n. These values, although somewhat smaller 

 than those given in table 10, can not be said to prove that low 

 temperature shortens the myoids as does high temperature. 



Gradenigro ('85) found that elevated temperature induced 

 a shortening of the rod in the dark. After measuring the myoid 

 length in a considerable number of preparations from retinas 

 subjected to various temperatures both in light and in darkness, 



