CONDITIONS INFLUENCING PREVALENCE 159 



populated Umfuli district. Being a skilled entomologist, 

 Mr. Marshall found several species of Anopheles in both 

 localities, and asks why the more populated district should 

 not be the more malarious. He forgets that Salisbury lies 

 nearly 5,000 feet above the sea, more than 2,000 feet above 

 the malarious regions, and that, though elevation per se is 

 no absolute bar to malaria, the temperature of places so 

 elevated, in that latitude south, is always too low for the 

 development of really serious malaria. Curiously enough, 

 we find that almost simultaneousl}^ another writer from 

 Mashonaland, Dr. Ch. Todd, demonstrating {Journ. Trop. 

 Med. 1900, p. 92.) that there, as elsewhere, the curve of 

 malaria prevalence follows that of rainfall and therefore of 

 Mosquitoes ; the most rainy months being January and 

 February, and the most feverish, March and April. 



Before proceeding to the consideration of the prophy- 

 laxis of malaria, it will be necessary to examine in detail 

 how far the prevalence of Mosquitoes and therefore of that 

 disease are influenced by climate, cultivation, and the other 

 incidents of everyday human environment. Working as I 

 have in India, it is natural that most of the examples cited 

 should be based on observations made in that country ; but 

 communications, personal and published, from observers in 

 other tropical regions, most of which cannot, however, be 

 quoted in any moderate space, convince me that our experi- 

 ence in that country may be taken as fairly typical of the 

 conditions present in other hot climates. 



It will be seen too that, with modifications arising from 

 the differences of oriental surroundings, I come to practi- 

 cally the same conclusions as Professor Celli, in his admir- 

 able work on " Malaria in Italy," and if I quote less than 

 might be expected from that work, it is partly because most 

 of the notes on which the present chapter is based were 

 written before I had an opportunity of reading it, but 

 mainly because I think that everyone interested in the 

 subject should make a point of reading his book in extenso. 



In certain cases, however, it is hardly practicable to 

 separate the consideration of the conditions favouring 

 malaria from the practical outcome of the facts noted, and, 



