CHAPTER I 



THE IMPORTANCE OF DOMESTIC FLIES 



THE discovery of the mode of transmission of the 

 malarial fevers by certain mosquitos was followed 

 by the practical application of the knowledge gained ; 

 the disease was prevented in many places by the 

 reduction of mosquitos. In several important centres, 

 for example on the Suez and Panama Canals, this disease 

 has been almost abolished. When it was proved that 

 yellow fever was carried by another species of mos- 

 quito, the domestic Culecine, these in their turn were 

 dealt with and reduced in many places and the disease 

 abolished, for example, at Havana, Rio, New Orleans, 

 Panama. But the discoveries concerning the trans- 

 mission of diseases by house-flies which have taken 

 place have not yet been followed by much practical 

 application, and but little organised attempt has been 

 made to reduce these insects too. This is partly 

 because the proofs of the damage done by flies are 

 not so thoroughly established as those concerning the 

 mosquito-borne diseases. As stated before, the house- 

 fly does not bite, and when it conveys disease it does 

 so accidentally, it is not possessed, as it were, of the 

 malice aforethought which the mosquito possesses in 

 her lust for blood ; the fly does not transfer the germs 

 of disease direct from the blood of one person to the 

 blood of another, but she takes the germs from the 



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