Mosquitoes and Malaria 191 



When the parasite became known there immediately arose specu- 

 lations as to the way in which it was transferred from man to man. 

 It was thought by some that in nature it occurred as a free-living 

 amceba, and that it gained access to man through being taken up 

 with impure water. However, numerous attempts to infect healthy 

 persons by having them drink or inhale marsh water, or by injecting 

 it into their circulation resulted in failure, and influenced by Leuckart's 

 and Melnikoff's work on Dipylidium, that of Fedtschenko on Dracun- 

 culus, and more especially by that of Manson on Filaria, search was 

 made for some insect which might transfer the parasite. 



Laveran had early suggested that the r61e of carrier might be 

 played by the mosquito, but Manson first clearly formulated the 

 hyopthesis, and it was largely due to his suggestions that Ross in 

 India, undertook to solve the problem. With no knowledge of the 

 form or of the appearance in this stage, or of the species of mosquito 

 concerned, Ross spent almost two and a half years of the most arduous 

 work in the search and finally in August, 1897, seventeen years 

 after the discovery of the parasite in man, he obtained his first 

 definite clue. In dissecting a "dappled-winged mosquito," " every 

 cell was searched and to my intense disappointment nothing what- 

 ever was found, until I came to the insect's stomach. Here, however, 

 just as I was about to abandon the examination, I saw a very delicate 

 circular cell, apparently lying amongst the ordinary cells of the organ 

 and scarcely distinguishable from them. On looking further, 

 another and another similar object presented itself. I now focused 

 the lens carefully on one of these, and found that it contained a few 

 minute granules of some black substance, exactly like the pigment of 

 the parasite of malaria. I counted altogether twelve of these cells 

 in the insect." 



Further search showed that "the contents of the mature pigment 

 cells did not consist of clear fluid but of a multitude of delicate, 

 thread-like bodies which on the rupture of the parent cell, were poured 

 into the body cavity of the insect. They were evidently spores." 



With these facts established, confirmation and extension of 

 Ross's results quickly followed, from many different sources. We 

 cannot trace this work in detail but will only point out that much 

 of the credit is due to the Italian workers, Grassi, Bignami, and 

 Bastianelli, and to Koch and Daniels. 



It had already been found that when fresh blood was mounted and 

 properly protected against evaporation, a peculiar change occurred 



