Gr. F. Petrie and C. R. Avari 
309 
TABLE III. 
Summarising results of examination of M. decumanus and M. rattus 
for trypanosomes. 
M. decumanus 
Males examined = 846I 0 , 
Males infected = 346) 0 
Females examined = 838) 43 . 30 / 
Females infected = 363 i 
Total*'examined =1832) gg.g 0 / 
Total infected = 724 J ' 0 
* Includes a number of rats i 
M. rattus 
Males examined =1273) 4 ( 5 . 50 / 
Males infected = 592 i 
Females examined = 1280 [ 
Females infected = 567 i u 
Total* examined =2651) 44 . 30 / 
Total infected =1188) ° 
which the sex was not noted. 
Surra examined 3105 M. decumanus and found 35 °/o infected. Our 
observations show that in 1905—1906, 40 —45 °/ 0 of the Bombay rats 
were infected. These results taken as a whole appear to confirm the 
conclusion arrived at by Laveran and Mesnil on experimental grounds 
in their work on T. lewisi that “ immunization through the placenta or 
by lactation is exceptional if it occurs at all.” At least the figures give 
no ground for belief that during a period of 20 years the rat population 
in Bombay has become less susceptible as the result of a cumulative 
hereditary transmission of immunity against the infection. 
Coming now to the consideration of the question of the seasonal 
prevalence of the infection, it is clear from the details given in the 
tables and represented graphically on the chart that a marked seasonal 
variation in prevalence exists, and that the curves of prevalence for 
M. rattus and M. decumanus present a noteworthy resemblance. Thus 
in the months June to December the percentage figures of infected 
animals of both species rise above the mean for the year, while in the 
remaining months the percentage figures fall below the mean. The 
lowest percentages of infected animals are found in March and April, 
corresponding to 6‘5 °/ 0 infected M. decumanus and 16'3 °/ 0 infected 
M. rattus, while the highest percentages appear from the chart to 
correspond to the month of August, in which 54'5 °/o Jf- decumanus and 
63'8 7o M. rattus proved to be infected. 
During the preparation of this paper for publication we have 
obtained a striking confirmation of these results while consulting 
Lingard’s original report (1895) of his observations on T. lewisi in 
Bombay. Lingard in this report ( Summary of Further Report on Surra, 
Bombay 1895) gives the data which led him to the conclusion that a 
