Vol. 8, 1922 
PHYSIOLOGY: W. F.HAMILTON 
351 
The method of conditioned behavior is not applicable to lower organisms 
and it meets with difficulties when applied to higher animals. There- 
fore, if we would study the evolution of reactions to color, we must cast 
about for another method. 
Most theories of color vision postulate receptive systems maximally 
sensitive to certain wave-lengths which differ in some manner from those 
which are maximally sensitive to other wave-lengths. The difference, 
according to some theories, lies in the receptive substance of the eye 
(Young-Helmholtz, Hering); according to others, there are different 
"color perceiving" mechanisms in the brain which serve for perception of 
the different fundamental colors. (Edridge Green, ^ Houstoun,^ and 
the various "Zone Theories.") Work on the human eye (Burch,^ Abney,^ 
Frank Allen^ and others) shows that these receptive systems can be sepa- 
rately fatigued by strong monochromatic light. 
If we can get evidence that the photo receptors of lower organisms can 
be differentially fatigued in a similar manner, it would indicate that the 
receptive system which is maximally sensitive to certain wave-lengths dif- 
fers in some respect from the receptive system which is maximally sensi- 
tive to other wave-lengths, and this could be construed into something 
analogous to color vision. The following is a preliminary report of the 
results of experiments recently performed with this in view. 
2. The animal decided upon was the fruit-fly, Drosophila. Specimens 
were kept in the dark over night and used in the dark adapted state. The 
apparatus consisted of two Hilger wave-length spectrometers** used as 
monochromatic illuminators and so set as to throw beams of light into op- 
posite ends of a small horizontal tubular glass cell containing the flies. 
The sources of light were two 500-watt Mazda C stereoptican lamps. 
The intensities of the light beams, differing as to wave-length were so 
regulated that the animals were not oriented in either direction. The lights 
were physiologically equal. As soon as this was accomplished one beam 
of light, called for convenience the "stimulating light," was intercepted by 
a screen and the animals subjected to the action of the other ("fatiguing") 
light. As soon as a marked decrease in the positive reaction of the flies 
to the "fatiguing" light was observed, the screen was removed and the ani- 
mals subjected to the "stimulating" light again. 
As soon as this was done, the animals usually oriented and crawled to- 
ward the "stimulating" light in spite of the continued action of the "fa- 
tiguing" light. The operation of the "fatiguing" light had thus upset the 
physiological balance between the two lights by fatiguing the apparatus 
maximafly sensitive to this light, more than the apparatus maximally 
sensitive to the "stimulating" light. When such a test had been com- 
plete, it was repeated immediately, with the light that had been used as 
