136 General Biology 



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 (of cities). We may easily 

 conceive that mosquitoes, 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 penetrating 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 marsh-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 persons 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 als'o 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, 

 came 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 

 arduous work following out experiments largely suggested by Manson. 



Finally, in August, 1897, seventeen years after the parasite was 

 first discovered in man, he obtained his first clue. 



While he was dissecting a "dappled-winged" mosquito and had 



