438 
Tryimnosortia lewisi 
11. The relation of Ectoparasites to the prevalence 
OF T. LEWISI IN RATS UNDER NATURAL CONDITIONS. 
Owing to the fairly constant association in nature of T. lewisi and 
fleas, it has been assumed that fleas are concerned to a considerable 
extent in the transmis.sion of the trypanosome from rat to rat. The 
association of T. leivisi with flea prevalence in rats has been demonstrated 
very clearly by Swingle (1907) and Nuttall (1908) and more recently 
by Petrie and Avari (1909) who report upon the examination of a very 
large material which was rendered accessible to them through the 
investigations of the Indian Plague Commission. Petrie and Avari 
found however that the prevalence of T. lewisi was inversely propor¬ 
tional to the flea prevalence, although so generally associated with it. 
The prevalence of Ileas on trypanosome-infected rats from Cherry- 
hinton Brook, Cambs, was very noticeable. On the other hand we 
failed to find a single flea on rats from Comberton, Cambs, or on 
20 rats imported from Berlin, none of which harboured trypanosomes. 
The species of fleas which we have found associated with M. decu- 
manus infected with T. lewisi are Ceratophyllus fasciatus, Ctenophthalmns 
agyrtes, and Pidex m'itans (one on one occasion in company with 
C. agyrtes). We have also captured on dogs Gtenocephalus cams 
harbouring parasites indistinguishable from T. lewisi. This species of 
flea is one which is also occasionally captured on the rat (Tiraboschi). 
Some observers believe T. lewisi is conveyed from rat to rat under 
natural conditions by the rat-louse {Haematopinus spimdosus Burm.), 
but no direct as.sociation has been recorded. 
Of the other blood-sucking ectoparasites which have been found on 
rats, none are likely to be more than occasional transmitters of trypanoso¬ 
miasis because they occur rarely on rats as compared with fleas and lice. 
The ectoparasites of rats are comprised in the following lists: 
Fleas found on Mus degumanus, M. rattus and M. muscvlus. 
(Given by Rothschild 1910, p. 89.) 
Dermatophihis 'penetrans., Linnaeus. 
„ caecata, Enderlein. 
Echidnophaga gallinoweus, Westwood. 
„ mynnecobii, Rothschild. 
,, murina, Tiraboschi. 
„ liopus, Rothschild. 
