298 Transmission of Trypanosoma lewisi 
Day 12. Blood examination positive : 3 T. lewisi found in a fresh 
blood film. 
Exp. IV. Three fleas ( Ctenopthalmus agyrtes) were removed from 
a heavily infected wild rat and immediately placed upon a clean white 
rat in a flea-proof cage. After 10 days (8—18. xii. 1908) many 
trypanosomes were detected in the white rat’s blood. 
In Experiment II a single flea failed to transmit T. leiuisi. In 
Experiments I and IY three fleas transmitted the trypanosome. In Ex¬ 
periment III it is reasonable to suppose that the trypanosome infection 
was due to the first batch of ten fleas which was placed on the experi¬ 
mental animal. The ease with which infection took place through the 
agency of fleas suggests that they are probably the chief transmitters of 
the trypanosomes. An extensive series of observations which we are 
at present making will however determine the relative importance of 
fleas and lice in the transmission of T. lewisi. 
(b) Transmission by lice. 
In four experiments carried out by Rabinowitsch and Kempner 
(1899) lice (species ?) were removed from rats harbouring T. lewisi in 
their blood. The lice were dissected and inoculated into clean rats, but 
the rats did not become infected. 
MacNeal and Novy (vi. 1903, p. 560) observed living T. lewisi in the 
stomach of lice (species ?), a statement which is repeated by MacNeal 
(xi. 1904, p. 520) who reports that in one experiment “several such 
lice” were transferred to a fresh rat (4. ii. 1904) with a positive result 
in that T. lewisi appeared in its blood after 14 days and persisted therein 
for five weeks. MacNeal was unable to observe anj^ development of 
T. lewisi in the rat-lice although he frequently observed the trypano¬ 
somes in them. He concludes therefore that “ the louse merely carries 
the protozoon from one animal to the other.” 
On the other hand Prowazek (1905, p. 365) described what he took 
to be the development of T. leivisi in the rat louse ( Haematopinus 
spinulosus Burmeister), but he failed to transmit the trypanosome from 
rat to rat by means of the lice. Nevertheless he concluded that these 
lice are certainly capable of transmitting the trypanosome. He ap¬ 
parently based this statement solely on the supposed development of the 
trypanosome in the rat louse. 
