440 
Trjipanosoma lew is i 
III. Experiments demonstrating the part played by Arthro¬ 
pods IN THE transmission OF T. LEWISI FROM RAT TO RAT. 
We have experimented with fleas {CeratophyUus fasciatus and 
Ctenophthalmus agyrtes), lice (Haematopinus spinulosus), bugs {Acanthia 
lectularia), ticks {Ornithodoros mouhata, nymphs and adults), and a 
Gamasid mite {Gamasus sp.). Only in the case of fleas did any trans¬ 
mission of T. leiuisi take place by the act of transferring the arthropods 
from an infected to a non-infected rat. The result of these experiments 
are recorded in the present paper. 
(i) Experiments with fleas. 
(а) By previous authors. Rabinowitsch and Kempner (1899) and 
Nuttall (1908) were the first to regard fleas as transmitting agents of 
T. lewisi and to demonstrate that they convey the infection, and their 
experiments have been confirmed by Minchin and Thomson (1910). 
Minchin and Thomson have recently proved that fleas if fed 
on an infected rat do not infect susceptible animals until about a 
fortnight afterwards. This is conveniently described as ‘distant trans¬ 
mission’ or ‘late infectivity of the fleas.’ The fleas then continue able 
to infect for a long time, possibly till the end of their life. From this 
it is obvious that fleas caught haphazard in nature may have already 
passed the latent non-infective period and may exhibit the power of 
distant continuous transmission. 
(б) Our experiments. In all of our experiments the arthropods 
were allowed to feed on an animal infected with T. lewisi, after which 
they were transferred to a clean animal, a variable interval of time 
being allowed to elapse before they were transferred from the infected 
to the clean animal. 
We performed 138 experiments with fleas and 22 of these (about 
16 Vo) gave a positive result. 
On adding up the numbers of the fleas which were used in the 
attempts to transmit infection, we find that 324 were used when 
positive results were obtained, while 1270 were used with negative 
results. That is, about 80 Vo were non-infective. Of the remaining 20 Vo 
concerned with the positive results it is safe to assume that some at 
least were also non-infective. 
