318 Trypanosoma lewisi 
that complete drying of blood containing T. brucei rendered the blood 
non-infective. Examination of Chart V from this point of view makes 
it clear that speaking generally the period of least prevalence of try¬ 
panosome infections in rats corresponds to the season of the year during 
which the humidity is below the mean for the year, viz. 75 (saturation 
= 100) while the period of greatest prevalence of trypanosome infections 
corresponds to the season during which the humidity is above the mean 1 . 
Chart Y. Showing the relation of trypanosome prevalence in Mus rattus to atmospheric 
humidity. 
- = T. lewisi in Mus rattus. 
.= Humidity (the mean = 75°). 
1 The rainy season in Bombay extends from June to October; the cold dry season 
comprising the months November to March, and the hot dry season the months April to 
the middle of June. 
