240 THE UNIVERSITY SCIENCE BULLETIN. 
matter. Now, these bugs, we will assume, have just been taken 
in nature. Their digestive tracts probably contain food ma- 
terial. A few are examined to determine this point. These 
are two factors at this beginning point to be considered. If 
the bugs have been feeding recently, the material in the diges- 
tive tract might be confused with food taken in from the food 
culture. Therefore the bugs must be divided into two lots. 
One placed in a sample of the given culture at once to serve 
as a check on normal (not starved) feeding, and the results 
observed. The other lot is then allowed to remain in the 
clear water for a time sufficient to clear much of the digestive 
tract. For this purpose fresh glass aquaria, with a few peb- 
bles placed on the bottom to which the bugs may cling, serve 
admirably. This lot, then, may be placed in another jar of 
the culture and allowed to remain for times varying from 
thirty minutes, for food selection, to weeks, for determining 
maintenance ability of the culture. In making the examina- 
tion the bugs are removed from the culture to distilled water 
for a few minutes. Petrie dishes do very well for this, be- 
cause they are shallow. By means of the forceps a bug is 
caught by one of its swimming legs and placed in a drop of 
water on a slide. After removing its head one dissecting 
needle is run through the thorax to hold it in position on its 
venter, and the other needle dissects out the digestive tract 
entire. The carcass of the bug is then removed, fresh, normal 
salt solution passed over the digestive tract, and notes made 
as to the general position of the contents, whether in some 
part of the stomach or in the intestine. Usually there will 
be two masses of material. The dissecting needle pricks the 
stomach wall to liberate the material, which promptly speads 
upon the slide. The other mass is removed in the same way, 
then the cover slip is added and both of these smears studied © ! 
under compound. Since the food is likely to be deep green 
in color, due to the plant chlorophyll, or at least to contain 
unicellular plant cells, or even bits of Spirogyra or Zygnema 
still containing plastids, it is convincing to make permanent 
mounts. To do this the smear is fixed in 8 per cent formalin 
to which has been added enough copper acetate crystal to give 
it a pale greenish tinge. This preserves the green color. The 
mount is then made in glycerine jelly in the usual way and 
sealed with asphaltum. Mounts made in this way can be used 
