12 STUDIES IN GENERAL PHYSIOLOGY 
The most extended experiments on the influence of light 
on the orientation of animals were made by Graber." His 
“comparative studies on light-sensations” (Vergleichende 
Licht-Gefihl-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 light 
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, 
1Grundlinien zur Erforschung des Helligkeits- und Farbensinnes der Thiere 
(Prag, 1884). 
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