88 
Trypanosoma leivisi, etc. 
body which remained perfectly rigid, while the flagellar end was 
attached to the gut-wall. Although I have never seen this parasite 
alive in the midgut of the flea, a group was discovered in a smear of 
the midgut which had been stained. 
The rectal contents always contained a vast number of the barley¬ 
corn-like cysts of the Crithidia. 
We have lately been successful in the Quick Laboratory in raising 
Ctenophthalmus agyrtes in large numbers, and it is hoped that we shall 
now be able to determine the complete life cycle of Gritliidia cten- 
ophthalmi. This flagellate was also found in one of the fleas from a 
rat uninfected with T. lewisi. 
Summary. 
1. The alimentary tracts of 104 lice ( Haematopinus spinulosus), 
which had been taken from rats infected with T. lewisi, were examined. 
In 51 lice no trace of T. leivisi could be found. In 53 lice T. lewisi, 
unchanged in every particular, was found in various parts of the gut. 
The trypanosome was seen to be quite unchanged in stained preparations. 
2. The alimentary tracts of 45 fleas {Ctenophthalmus agyrtes), which 
had fed on infected rats, were examined. The T. lewisi could not be 
found at all in 43 fleas. They disappeared very rapidly from the 
ingested blood and could not be found in stained preparations. In 
2 fleas trypanosomes were found, but they did not differ in form from 
those seen in the blood of the rat. 
3. 263 lice were examined from rats which were apparently unin¬ 
fected with T. lewisi. No form of T. leivisi was discovered in fresh or 
stained preparations. 
4. 31 fleas from uninfected rats were dissected and their alimentary 
tracts examined. No trace of T. lewisi was found. 
5. 15 lice were examined 18—48 hours after their removal from 
an infected rat. T. leivisi was found in 7 of these, but they shewed no 
developmental changes. 
6. Observations made upon 36 lice from infected rats shewed that 
at the earlier stages of digestion T. lewisi was more often found than at 
the later stages. In some lice however trypanosomes could not be found 
at the early stages of digestion, although they were present at an 
advanced stage of digestion. 
7. The examination of other organs than the alimentary canal in 
fleas and lice did not shew any form of T. leivisi. 
