THE PROTOZOA 135 



8. In malarial districts the use of fire, both indoors and to those 

 who sleep out, affords a comparative security against malaria, because 

 of the destruction of mosquitoes. 



9. It is claimed that the air of cities in some way renders the poison- 

 innocuous, for, though a malarial disease may be raging outside, it does 

 not penetrate far into the interior. We may easily conceive that mos- 

 quitoes, while invading cities during their nocturnal pilgrimages, will 

 be so far arrested by walls and houses, as well as attracted by lights in 

 the suburbs, that many of them will in this way be prevented from pen- 

 etrating "far into the interior." 



10. Malarial diseases and likewise mosquitoes are most prevalent 

 toward the latter part of the summer and in the autumn. 



11. Various writers have maintained that malaria is arrested by 

 canvas curtains, gauze veils and mosquito nets, and have recommended 

 the use of mosquito curtains, "through which malaria can seldom or 

 never pass." It can hardly be conceived that these intercept marsii-air 

 but they certainly do protect from mosquitoes. 



12. Malaria spares no age, but it affects infants much less fre- 

 quently than adults, because young infants are usually carefully housed 

 and protected from mosquito inoculation. 



King's work does not seem to have come under the notice of the 

 European and Asiatic workers, so it was not until 1894 that Sir Patrick 

 Manson, who had done pioneer work in filariasis (See Chapter XX), 

 came to the conclusion that there must be an intermediate host for a 

 parasite so similar in its general functioning as malaria is to filaria. 



It was already known that long thread-like processes formed as 

 soon as the parasite escaped from the blood, and became free-swimming 

 in the surrounding media. 



At first it was thought that water containing the parasite was the 

 carrier of infection but no one who drank the water developed malaria ; 

 in fact, they did not even develop the disease when this water was 

 actually injected into the veins. 



Manson then suggested that these motile forms must have some- 

 thing to do with the manner of communicating the disease, and it was 

 he who also thought a blood-sucking insect the most likely intermediate 

 host. After so much progress had been made it was a simple matter 

 to think of the old association of mosquitoes and malaria. 



It is interesting to note also, that Laveran working independently, 

 come to similar conclusions in the same year that Manson did. 



Major Ronald Ross, in India, without any knowledge of the form 

 or appearance of the parasite during the time it is developing within 

 its intermediate host, and without a knowledge of the species of the 

 insect he was looking for, spent two and a half years of intensely ardu- 

 ous work following out experiments largely suggested by Manson. 



