12 STUDIES IN GENERAL PHYSIOLOGY 



The most extended experiments on the influence of light 

 on the orientation of animals were made by Graber. 1 His 

 "comparative studies on light-sensations" (Vergleichende 

 Licht-Gefiihl-Studien), as he called his investigations, cover 

 about fifty species. His method is that followed by Lub- 

 bock. 



The faultiness of this method and the errors of interpre- 

 tation of the results obtained stand out more clearly in 

 Graber' s writings than in Lubbock's. Graber covers one- 

 half of a vessel with a partially or completely opaque 

 screen, and after a time notes how the animals are dis- 

 tributed in the vessel. If most of the animals are under 

 the opaque screen, Graber says that they are "fond of the 

 dark" and "hate the light;" or in the reverse case, that 

 they are "fond of the light" or of "the white" and "hate the 

 dark." He therefore uses the conceptions of "white" or 

 "bright" and "dark," which designate certain effects of liylii 

 upon a human being for the conceptions of great or small 

 intensity of the light; and in saying that animals which 

 "prefer the light" also "hate the darkness" he makes a 

 second mistake in that he maintains that strong and weak 

 light have opposite effects. We shall see, however, that 

 these effects are similar and differ only in degree. He makes 

 the same mistake in experimenting on rays of different 

 refrangibility. The most important among the facts ob- 

 served by him in this connection is this, that animals which 

 "prefer the light" with a few exceptions also "prefer" blue, 

 while those which "hate the light" "prefer" red. His ideas 

 are expressed in the following remarks, which, however, I 

 do not fully understand: 



The question arises as to the cause of this truly striking rela- 

 tion between the love for white light and for blue light, on the one 

 hand, and between the dislike for white light and for blue light, 



i Grundlinien zur Erforschung des Helligkeits- und Farbensinnes der Thiere 

 (Prag, 18&4). 



