TRYPANOSOMES IN TSETSE-FLIES AND OTHER DIPTERA, 167 
partially withdrawing the proboscis from the skin of its victim, 
and then lowers it again.! Probably when the proboscis is 
lowered the sucking stomach is being filled, and when it is 
raised the blood is being expelled from the sucking stomach. 
This would account for the traces of blood found in the suck- 
ing stomach, and also in the proventriculus and thoracic intes- 
tine, after a meal. If the fly over-fed itself, it might not be 
able to discharge the last bolus of blood from the sucking 
stomach. 
When the digestive tract is gorged with blood it is so dis- 
tended, and the wall is so thin, that it is a difficult matter to 
dissect it out without rupturing it and letting blood escape. 
My colleagues, Gray and Tulloch, taught me a simple and 
effective method for doing this operation, which is as follows: 
The terminal segment of the abdomen is snipped off, the body 
is laid flat on an ordinary shde, and then a mounted needle, 
seeker, or other suitable instrument, is pressed down flat on 
the waist or base of the abdomen and passed along with an 
even, steady pressure towards the tip of the abdomen, so as to 
squeeze all the contents of the abdomen out on to the slide. 
With a little care and practice all the abdominal organs can 
be squeezed out quite uninjured, and can be separated from 
one another on the slide afterwards. In most cases the 
thoracic intestine and proventriculus are pulled out together 
with the abdominal contents. This simple method is most 
useful for rapid examination of a number of flies. 
In order to make smears of the stomach-blood, it is neces- 
sary, as already stated, to mash it up with a little salt-citrate 
solution; for the intestinal and proctodzeal contents this is 
not necessary. Itis best to avoid, as much as possible, the 
use of salt-solutions. By comparing preparations made from 
pure blood with those of blood that had been mixed with 
citrate solution, I found the trypanosomes distinctly altered in 
form in the latter. Our method was to draw up the intestinal 
1 Der Riissel wird... wahrend des Saugens haufig sagend auf- und 
abbewegt,” Stuhlmann (41, p. 4). My statements in the text were written 
before Stuhlmann’s memoir came to hand. 
