MOVEMENTS IN THE VISUAL CELLS 141 



the external limiting membrane. These workers were primarily 

 interested in discovering mider what conditions of temperature 

 an accumulation of pigment in the rod area could be avoided, 

 for their investigation dealt with the visual purple. Since the 

 frogs used for these determinations were treated with curare 

 in order to produce pigment relaxation, and, moreover, since 

 these animals were in an oedematous condition as a result of this 

 poisoning, it is evident, as Herzog ('05) pointed out, that much 

 weight can not be given to their conclusions alone. 



To Gradenigro ('85) belongs the credit of having performed 

 the first temperature experiment upon the retinal pigment of 

 normal animals. He introduced a dark-adapted frog into a 

 dry, darkened chamber and removed the whole to a dark room. 

 A temperature of 30°C. was maintained until heat rigor set in, 

 when, on examination, the pigment was found to be in a condi- 

 tion of maximal light expansion (fig. 19). Gradcnigro's results 

 were confirmed by Angelucci ('90) and by Fujita ('11). 



Herzog ('05), without knowledge of Gradenigro's contribution, 

 undertook a detailed study of the relation between temperature 

 and pigment distribution. His results not only corroborated 

 those of Gradenigro, but also estabhshed the additional facts 

 that at low temperatures (0°-14'C\) in the dark the distribu- 

 tion of pigment is identical with that at high temperatures 

 (fig. 17), while only between 14° and 18°C. in the dark (fig. 18) 

 is maximal pigment contraction obtained. 



His experiments were performed in the following manner. 

 Dark-adapted frogs (R. temporaria and H. esculenta?) were 

 placed in a heating chamber at an initial temperature of 20°C'., 

 the introduction of the animals cooling the apparatus to 17°-18°C'. 

 Progressive heating raised the temperature in 15 minutes to 

 24°C., in 30 minutes to 32°C., in 45 minutes to 37°C., and in one 

 hour to 39-40°C. At each fifteen minute interval frogs were 

 removed and their eyes prepared for microscopical examination. 



At 24°C. the position of the pigment was not essentially dif- 

 ferent from the normal state of maximal contraction, although 

 delicate fringed processes did extend towards the external Um- 

 iting membrane. It is probable that such an experiment did 



