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THE TRANSMISSION OF TRYPANOSOMA LEW I SI 
BY FLEAS AND LICE 1 . 
By GEORGE H. F. NUTT ALL, F.R.S. 
(a) Transmission by fleas. 
The first experiments upon the transmission of T. lewisi by fleas 
were carried out by Rabinowitsch and Kempner (1899) who observed 
that three fresh rats placed with others harbouring trypanosomes in 
their blood subsequently (after 11—15 days) became infected. Fleas 
(species ?) were found on these rats. They next teazed the bodies of fleas 
taken from infected rats and inoculated them into fresh rats with the 
result that in five out of nine experiments the fresh rats became infected 
with T. lewisi. In one experiment they removed 20 fleas from infected 
rats and placed them on a clean animal with the result that the latter 
became infected after 2—3 weeks. They regarded this one experiment 
as conclusively proving that T. lewisi is transmitted by rat fleas. 
Swingle (v. 1907, p. 119), who supposed he had observed a develop¬ 
ment of T. lewisi in rat fleas (species ?), cites some indirect evidence 
which indicates that fleas play an important part in the transmission 
of the trypanosome. Of 17 one-fourth grown rats examined in the 
autumn and winter not one harboured lice, fleas or trypanosomes. Of 
seven rats examined in the spring, at the same place, all harboured 
fleas and four harboured trypanosomes. Rats captured in other parts of 
Lincoln, Nebraska, harboured neither fleas, lice, nor trypanosomes. Fleas 
were found more frequently than lice on trypanosome-infected rats. 
The single experiment by Rabinowitsch and Kempner has hitherto 
constituted the sole proof that fleas transmit T. lewisi. I desire 
to record confirmatory experiments which were carried out with every 
precaution so as to exclude any other mode of infection. 
1 Read before the Cambridge Philosophical Society, 23 Nov. 1908. The third and 
fourth experiments with fleas have been added. 
