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ON THE SEASONAL PREVALENCE OF TRYPANOSOMA 
LEW I SI IN MUS RATTUS AND IN MUS PEGU MANUS 
AND ITS RELATION TO THE MECHANISM OF TRANS¬ 
MISSION OF THE INFECTION. 
By G. F. PETRIE, M.D., and C. R. AVARI. 
No precise observations so far as we are aware have been published 
hitherto regarding the seasonal prevalence of any of the infections 
in man or animals—malaria excepted—which are definitely associated 
with the presence in the blood of the host of a protozoan. For this 
reason we have thought it desirable to record an extensive series 
of observations on the occurrence of T. lewisi in M. rattus and M. decu- 
vianus in Bombay made during a period of 14 months in the years 
1905—1906. 
A recent paper by Nuttall (1908) on the transmission of T. lewisi by 
means of insects has revived interest in the question of the mode of 
transmission of this parasite from rat to rat. We believe that our 
observations have a bearing upon this problem and we shall therefore 
bring under review in due course the epidemiological factors which must 
be reckoned with in a discussion of the problem. 
While reserving full discussion of these factors until later it may be 
stated at once that evidence will be brought forward which points to 
a developmental cycle taking place in the insects transmitting the 
infection. This evidence, derived as it is from purely epidemiological 
sources, is perhaps of especial interest in view of Kleine’s (1909) 
important experiments on the transmission of T. brucei confirmed 
recently for T. gambiense by Bruce (1909)—experiments which make 
it practically certain that these trypanosomes undergo a cycle of 
development in the Glossina palpalis. Moreover our observations 
seem to us to shed some fresh light on the transmission of T. letvisi 
and probably also of all insect transmitted trypanosomes in that they 
give a clue to the dominant factor influencing the cycle of development. 
Parasitology ii 20 
