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BULLETIN: MUSEUM OF COMPARATIVE ZOOLOGY. 
III. Observations. 
1. ReEAcTIONS TO SINGLE MONOCHROMATIC LIGHTS. 
A. Reactions with both the Skin and the Eye as Receptors. 
In testing the reactions of toads to single monochromatic lights 
the combined generators, as described on p. 261-262 were used. 
These generators were so adjusted as to give out lights of the same 
wave-lengths, and screens were so arranged that one or the other hght 
could be cut off in the dark chamber. The lights employed were those 
already described on p. 259. 
Twelve toads were successively tested in each light, and each animal 
was given eight trials, of which four were made in the light from one 
generator, and four in that from the other. The total number of 
trials in each light was therefore 96. The twelve toads were always 
brought into the experimental dark-room the afternoon before the 
experiments were made, and care was taken that they should not in 
any way be illuminated until they were exposed to the light in which 
they were to be tested. They were thus subjected to a condition of 
dark for at least fourteen hours before being tested, and at the time of 
the test they were undoubtedly “dark adapted.” After a toad had 
been tested in a certain light, it was again placed in the dark, and was 
not experimented with for at least an hour, after which period its 
reactions in another light were tested. I do not think that there can 
be any doubt that the toads were thus always “‘dark adapted” for 
each set of tests. 
The procedure used in the experiments was as follows: the lights 
from both generators were tested spectroscopically and photometri- 
cally; after they had been found to be equal, that from generator B 
was screened off, and that from generator A admitted to the dark 
chamber. Toad No. 1 was then placed on the table, in the beam of 
light from generator A, and held with its head toward the observer. 
Before any reaction could be made, it was quickly rotated through 
180 degrees, so that its head was directed away from the observer, and 
it was freed in this position, with the light impinging on its left side 
and at right angles to its long axis. At each of the succeeding trials, 
the toad was rotated clockwise, so that for the second trial it was 
headed toward the observer, with the light impinging on its right side; 
for the third, away from him, ete. After a total of four trials had thus 
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