108 INSECTS AND DISEASE 
microgametes. These, four to six in number, are rapidly 
shot out from the surface. They contain the nuclear 
chromatin, that is the portion concerned in reproduction, 
and lash wildly about, finally breaking away and swimming 
in a serpentine fashion, until they find and conjugate by 
fusion with one of the female cells. The fertilised cell 
develops into a rather elongate motile worm-like individual, 
which pushes its way through the epithelial lining of the 
mosquito’s stomach. There it becomes a spherical, motionless 
rapidly-growing cell in a cyst-like envelope. The nucleus 
divides as it increases in size, and each daughter-nucleus 
again divides until the cell becomes filled with a crowd 
of spores, from some hundreds to over ten thousand, which 
are set free by the bursting of the cyst. The spores are 
minute spindle-shaped actively motile bodies. They are 
carried in the body-fluid of the mosquito until they reach 
its salivary or poison glands, which are filled with them. 
When the mosquito next takes a feed they pass down its 
proboscis into the blood-vessels of the man bitten. In his 
circulation, they develop according to the sexual cycle 
from which we started. 
Now that this really marvellous life-history has been 
fully elucidated, there can be no doubt in the mind of any 
biologist that malaria is propagated by the mosquito ; 
and we have no evidence that it can be propagated in any 
other way. This conclusion has been confirmed by rigorous 
experiment. Mosquito-proof huts have been erected in 
the most malarious parts of the Roman Campagna, and 
observers living in them throughout the fever season, have 
remained free from malaria. On the other hand, mosquitos 
which have been allowed to bite a malarious patient in 
Rome have been sent by post to London, and have there 
successfully infected an Englishman, who had never visited 
a malarious district. Already the knowledge acquired 
has borne practical fruit. We may free a district from 
malaria (1) by treating all the inhabitants of a district, 
including especially all the children, by quinine in sufficient 
doses to exterminate the malaria parasites in their human 
cycle. This method has been pursued with some success 
by Professor Koch, but the difficulties in pursuing it with 
thoroughness are immense, and unless thorough it is useless. 
