230 Transactions. — Miscellaneous. 



A practical result of this decision that parasitic bodies 

 were the cause of malarial fever was investigation as to their 

 origin, whence and how they reached the blood of man. This 

 question baffled all observers for many years. The clue to 

 its solution was given by the observation that some of the 

 malarial parasites in specimens of blood examined some 

 minutes after its removal from the body exhibited a change, 

 in which processes (" flagella ") grew out from them, these 

 processes finally separating from the parasites and moving off 

 on their own account. 



Now, some living creatures of a low order have the pecu- 

 liarity that their life-cycle varies with their environment, and 

 it was known that some organisms very similar to this pro- 

 tozoon of malaria developed under special circumstances just 

 such moving bodies as these flagella as the first stage of a 

 new cycle of development. This was suggestive. There 

 must, of course, be some purpose served by these flagella, and 

 that purpose apparently had nothing to do with the life of 

 the parasite within the body of man, since their appearance 

 was always subject to the removal of the parasites from the 

 body. Granted so much, and it followed that the malarial 

 parasite had a second life-cycle apart from man of which 

 these flagella were a necessary phase. It was Dr. Manson 

 who argued thus, and he went still further. He was of 

 opinion that the only natural means by which the parasite 

 and the blood containing them was likely to be removed from 

 man was through the agency of some blood-sucking insect. 

 He suggested the mosquito. He was biassed in favour of 

 the mosquito, because he had already shown that it was the 

 intermediate host of another human parasite, a minute worm 

 called Filaria. 



(I may state here that there was a long-standing tradition 

 among the peasants of Italy that malaria and mosquitos were 

 in some way connected ; and among certain tribes in German 

 East Africa not only is the same belief held, but the same 

 word is used both for malaria and the mosquito.) 



Manson suggested that when the mosquito had sucked 

 malarial blood the parasites developed these flagella in the 

 stomachs of the insects, and these moved off through the 

 stomach-walls to other parts of their bodies, and then in 

 some way, after further development, once more reached a 

 human host. Manson suggested that the mosquito either 

 died in water or that its body was washed or blown into 

 water which was afterwards drunk by a man ; but this part 

 of his theory proved incorrect. Manson was in London him- 

 self, and had no opportunity of experimenting to test his 

 theory, but his lectures made a great impression on an 

 army surgeon named Ross, who had already done some 



