514 Col. Sir D. Bruce and others. Development of [Feb. 15, 
three changes of normal saline solution, in order to minimise the chance of 
their being contaminated by accidental rupture of the intestines. 
The stained specimens were examined day after day, and coloured 
drawings, at a magnification of 2000 diameters, made of all the different 
forms met with. The drawings of the trypanosomes found in the proboscis, 
proventriculus, fore-gut, mid-gut, hind-gut, proctodzeum, and salivary glands, 
were kept separate, so that a series of drawings of trypanosomes taken from 
any one part, from the first day of infection to the 56th day, could be 
compared. 
By arranging these drawings on a wall the horizontal layers would 
represent the contents of, say, the fore-gut from one day onwards, while the 
vertical rows would represent the trypanosomes found in the whole length 
of a fly for one day. More than six hundred drawings were made in this 
way, so that 16 seems impossible that any important form can have been 
left out. 
GENERAL CONSIDERATIONS REGARDING THE DEVELOPMENT OF THE TRYPANO- 
SOMES IN THE FLY. 
Let us now take a general view of the types of trypanosomes found in the 
various parts. It is evident that very few of the six hundred drawings can 
be reproduced; a few types, taken here and there, must suffice. For the 
first three or four days trypanosomes are found in all the flies, but at the end 
of six or seven the trypanosomes have disappeared out of many of them. 
That is to say, it is only in a certain percentage that further development 
takes place.’ In one series this was 8 per cent. In 92 per cent., then, 
of flies which imbibe infected blood, the trypanosomes simply degenerate and 
die out within the first few days. In 8 per cent., on the other hand, the 
trypanosomes find conditions more favourable for development, and increase 
to a marvellous extent, filling the whole of the fore-gut, mid-gut, and 
hind-gut with countless swarms of trypanosomes. 
How long this development continues is unknown. It is considered 
probable that it continues for the remainder of the fly’s life, and this has 
been proved by experiment up to 96 days. 
What the conditions in the intestine of the fly are, which render this 
development possible, are also unknown. It was thought that it might 
depend on the reaction of the intestinal fluids. This is, however, found on 
examination to be faintly acid in all flies, whether development has taken 
place or not. The presence of bacteria also seems to have no connection 
with the phenomenon. Sex, moreover, has no influence; development occurs 
in as many males as females. | 
