Gr. F. Petrie and C. R Ayari 
311 
Chart II. Showing prevalence of trypanosomes in Mus decumanus, Bombay, 1894, 1895. 
(Constructed from Lingard’s figures.) 
With regard to the interpretation of these curves we cannot but 
believe that this is bound up with the mechanism of transmission of the 
infection. The present state of knowledge on this subject does not 
justify us in bringing forward any positive conclusions in the matter. 
Nevertheless some considerations may be advanced here which in our 
view assist in explaining the facts narrated above. 
If it be admitted that the explanation of the variations in prevalence 
is probably to be found in the mode of transmission of the parasite, 
two hypotheses suggest themselves as affording a reasonable inter¬ 
pretation of the facts. The first hypothesis is that the trypanosome 
prevalence is associated with a seasonal prevalence of the insects trans¬ 
mitting the infection, and the second possibility is that apart from 
insect prevalence the conditions for successful transmission of the 
infection by insects vary at different seasons of the year. 
