Ill 



THE CARRIAGE OF DISEASE BY FLIES 



IT 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 (Aedcs 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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