486 'Journal of Comparative Neurology and Psychology. 



mucilage. To reduce the flies to a temporary state of insensi- 

 bility and quiet, during which the covering to the eyes could be 

 applied, recourse was made to what might be called a natural 

 anesthetic. If Drosophila is exposed for a short time to a tem- 

 perature of 0° C. its movements cease, and it becomes apparently 

 insensible. If then brought into the ordinary temperature of the 

 laboratory several minutes will elapse before it recovers, and 

 during this time the operation of covering the eye may be per- 

 formed under a dissecting microscope. When the recovery takes 

 place it appears to be a complete one, the fly responding in a 

 normal way to all stimuli. Since a low temperature must often 

 be present in the insect's natural environment, it may be supposed 

 that the action of cold will be attended with less risk of altering 

 the nervous system than that of the chemical anesthetics usually 

 employed.^ 



Repeated trials made with flies thus deprived of the sight of one 

 eye showed that under such conditions of unsymmetrical stimu- 

 lation they, nevertheless, crept in a fairly direct path toward the 

 light, although a tendency to deviate toward the side of the normal 

 eye regularly occurred. The insects generally moved in a peculiar, 

 jerky manner. The tendency to diverge from the direct path 

 toward the side of the uncovered eye was overcome by a series of 

 short, quick turns in the opposite direction, which kept them 

 headed toward the light. Normal flies, used as a control, pursued 

 straight courses, and usually reached the end of the container 

 before the experimental flies. Now and then one of the partially 

 blinded flies performed circus movements; but this conduct was 

 exceptional, and was never persisted in except in the case of a 

 single insect, which had long been active, and showed signs of 

 fatigue. 



It is clear that the tropism theory, with its assumption of a local 

 action of the stimulus on the side exposed to its eflPect, does not 

 furnish a complete explanation of these reactions. Though the 

 persistent tendency to turn toward the side of the functional eye 

 gives some evidence of a purely mechanical reaction to a local 

 stimulation, such a reaction is evidently inhibited and dominated 



1 The resistance of Drosophila to cold is rather remarkable. I have buried a glass vessel containing 

 thirty-three flies in a snow-bank over night, exposing them thus to a temperature of about 0° C. for 

 seventeen hours. Of these thirty-three, all except five recovered when brought again into the ordinary 

 temperature of the laboratory. 



