REACTIONS TO LIGHT AND GRAVITY IN DROSOPHILA 53 
METHODS USED FOR MEASURING REACTIONS 
The following were the chief systems devised for measuring 
the phototropism of flies with the above apparatus. The in- 
sects to be tested were taken from the breeding bottle and ether- 
ized. ‘Those to be tested were then isolated and placed in small 
vials with or without food, according to the detailed conditions 
of the particular experiment. When about to be tested, unless 
otherwise indicated, the flies were always light adapted, after 
which they were introduced into the large testing tube. At first 
this was done by means of a funnel, but later on the vials were 
Fig. 1. A, First box containing 200 watt lamp. B, Second box to the front 
of which is fastened the outer flask D, containing either clear water or colored 
liquids. C, Inner flask fastened to front of first box, and always containing clear 
water. #, Tube divided into fifths valued as indicated for the purpose of cal- 
culating the tropic indices. /', Black screen to shield tube from stray light rays. 
padded so that the mouths would just fit into that of the tube, 
into which the insects were allowed to crawl with as little shaking 
as possible. When the flies had been attracted into the proper 
end the tube was slipped into position and the test begun. If 
agitation was desired, a lever which released the pendulum was 
struck the instant that the tube was in place. When the test 
in question was completed the flies were replaced in their origi- 
nal position as follows. The tube was taken before a window or 
bright lamp and gently tapped with the fingers or twirled be- 
tween them. If this method failed, as in the case of non-photo- 
tropic flies, shaking was resorted to. Variations of this sort 
will be mentioned in connection with the experiment under 
discussion. 
‘ 
