August, ’24] GLASER: REARING FLIES FOR EXPERIMENTAL WORK 491 
the liquid to hang down on the reverse side of the top. This, naturally, 
is a great aid to the flies in obtaining a sufficient amount of food. The 
food is tendered for about 15 to 20 minutes. During this time all flies 
requiring food will have fed. The remaining fluid is then absorbed with 
absorbent paper towels and the tops (left in place) are scrubbed with hot 
water by means of a stiff hand brush. 
If a new brood of adults is to be used for study instead of breeding, 
individuals may be isolated or a certain number of one sex or of both 
sexes segregated. For this purpose the wide-mouthed, six-ounce bottles 
shown on Plate II, Figure 4 are employed and a breeding medium may 
be first introduced should this be desirable. The transfers from the breed¬ 
ing jar are effected as previously described and the desired flies placed 
in the experimental bottles while under anesthesia. Cotton gauze tops 
held in place by rubber bands keep the flies from escaping. A bell or 
battery jar, as shown in the figure, may also be placed over the bottles 
to keep wild stray flies from contaminating the tops. 
The flies in the experimental bottles are fed by permitting the liquid 
or semi-liquid food to drop upon the cotton gauze tops from pipettes... 
Three drops from an ordinary pipette are usually sufficient for from six 
to twelve flies. The third drop usually falls through, which is a good 
thing, since two or three individuals in a bottle always seem to prefer 
to take their food at the bottom instead of at the gauze top. Feeding, 
engorgement with the consequent tremendous swelling of the abdomen, 
and the passage of feces later are all indications that the food offered 
has been accepted. 
As a matter of routine, the flies subjected to experimentation were 
transferred to fresh sterile bottles three times a week and fresh tops 
replaced the old ones. However, if a particular bottle became unduly 
soiled the flies were transferred to a fresh bottle as soon as the condition 
was noticed. It is important to watch the bottles, because flies become 
soiled easily with liquid or semi-liquid food, especially when old and 
weak. When in this condition they frequently stick to the glass where 
they die of hunger or exhaustion. When found in this predicament and 
still alive, they can be saved by removing them with-a pair of blunt 
forceps and washing them off under a gentle stream of lukewarm water 
from the tap. In most cases flies so treated will recover and appear 
normal the next day. 
Experience in using both the experimental bottles and the breeding 
jars has shown that it is necessary to feed adult flies daily without ex¬ 
ception. No advantage is gained by feeding M. domestica or Stomoxys 
