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 
amoeba, 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 role 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 
w r ork 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 
