Ill 
THE CARRIAGE OF DISEASE BY FLIES 
I T would probably be impossible to trace the first sug¬ 
gestion of the carriage of disease by flies. They 
have been conspicuously connected with accounts of 
epidemics of one kind or another for hundreds of years, 
and before discussing some of the specific diseases 
which they are thought to carry some attention may be 
given to some of these early suggestions. It should 
be pointed out before taking up this subject, however, 
that the house fly is simply a carrier of disease germs, 
and that it differs in its relation to disease from the 
malarial mosquitoes, which are the necessary secondary 
hosts of the causative organisms of malaria, in that 
only in mosquitoes of the genus Anopheles can the 
germs complete their life round and develop sexual 
forms. 
In this they differ also from the yellow fever mos¬ 
quito (Aedes calopus), since, although the causative 
organism of yellow fever has not yet been discovered, 
close analogy shows that it must be a protozoan de¬ 
pendent for its full development upon a lodgment in 
the stomach of the mosquito in question. It differs 
in the same way from the bedbug, which has more re¬ 
cently been seen to be probably the necessary secondary 
host of the causative organism of kala azar. The house 
fly simply carries the germs of disease, either on its 
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