﻿70 DR. J. W. SCOTT MAGFIE— EXPERIMENTS AND 



stupefaction produced b y chloroform the process of digestion appeared to be 

 arrested. The following is an example of one such experiment : — 

 One male and one female G. palpalis, lean and unfed. 

 12 noon. Stupefied and weighed — *038 gm. 



1.0 p.m. Flies completely recovered; 



1.30 Allowed to feed on my finger, which they did readily, stupefied 



with chloroform as soon as they ceased feeding, and weighed 

 —•088 gm. 



Therefore the blood taken up by one fly was : — (*088 — *038)-i-2, or *02o gm. 

 As the result of a number of such experiments the average weight of blood 

 ingested by the male was found to be "027 gm. which, reckoning the specific 

 gravity of normal blood as 1*06, corresponds to 2*5 cmm. Larger numbers of 

 flies were not employed in each experiment owing to the difficulty of getting them 

 to feed simultaneously, and the practical impossibility therefore of preventing 

 some of them exuding drops of fluid before being weighed. The advantage in 

 the reduction of the one source of error would therefore have been overbalanced 

 by the introduction of another. 



The weight of the flies varies considerably with the length of time 

 that has elapsed since the last meal, but nevertheless there is an appreciable 

 difference between the weights of the unfed males and females. As a rough 

 average the unfed male weighs *020 gm., and the female, which is somewhat 

 larger, *028 gm. The same applies to the fed flies — they do not always engorge 

 themselves to the same extent, but the average weight of blood ingested is some- 

 what greater in the case of the female. On one occasion as much as *0485 gm. 

 (or 4'5 cmm.) of blood being drawn up by a female, and *030 gm. by a male. 

 The proportion is perhaps better stated in comparison with the body weight — a 

 male G. palpalis is capable of sucking up blood weighing 1*3 times his body 

 weight, and a female 1*6 times her body weight. 



With regard to the frequency with which the flies feed it was generally found 

 that once fed they refused to bite again until about 30 hours had elapsed. But 

 here again the intensity of the last meal has to be taken into account, for on one 

 occasion a fly which had fed very fully refused to feed again until 70 hours later. 

 As the flies were all confined in glass jars containing no water this shows that 

 when fully and naturally fed they are able to live unfed much longer than 

 the 30 hours that is sometimes given as the limit of their endurance under such 

 conditions. 



Digestion. 



Having fed, the tsetse-fly settles quietly to digest. At first the under surface 

 of the distended abdomen is uniformly red in the case of the male, but the female 

 always has a pale opaque spot at the distal end. In from 2 to 5 minutes however 

 a pale bubble appears at the proximal pole situated generally just to the left of 

 the mid line. This bubble shows slight movements of contraction and expansion 

 as though it were influenced by some peristaltic-like action of the bowel, and 

 moves gradually over towards the left side, keeping all the time at the proximal 

 extremity of the abdomen. On dissecting a fly at this stage, the bubble was 

 found to be gaseous, and from the fact that the red tint of the blood lingers along 



