CONDITIONS INFLUENCING PEEVALENCE 



165 



down the temperature, and so shortening or abrogating the 

 period of immunity due to heat, and that the more evenly 

 it be distributed the more serious will be its effects on 

 public health. 



So greatly is malaria favoured by a copious rainfall that 

 in the majority of places the monthly incidence of neio infec- 

 tions of malaria may he roughly said to he directly 'propor- 

 tional to the rainfall of the preceding month. The only 

 apparent exceptions to this rule occur in places where a 

 heavy rainfall occurs during months too hot or too cold for 

 the development of the parasite ; but of course in such 

 places the rule must be taken to apply only to those months 

 during which the air temperature permits of the maturation 

 of the parasite within the Mosquito. Without encumbering 

 these pages with needless statistics, the two following exam- 

 ples may be taken as fairly typical, remembering always 

 that the figares given probably include a much larger number 

 of recurrent than of primary attacks. 



Table Showing the Relation op Rainfall to Admissions to Hospital 

 FOR Malarial Fever (including Recurrent Cases) in Two Indian 

 Prisons. 



The figures referring to the Nagpur Central Jail are 

 derived from a paper by Major A. Buchanan, I. M.S., pub- 

 lished in the Indian Medical Gazette, and both series 

 represent the averages of ten years. In the case of the 

 Shahjahanpur Jail the average strength of prisoners during 

 the period was 378"7. 



Conditions of atmospheric pressure can, per se, have no 

 influence on the incidence of malaria. 



