PAET V 



THE RELATION OF HOUSE-FLIES TO DISEASE 



CHAPTER XX 



THE DISSEMINATION OF PATHOGENIC ORGANISMS BY FLIES 



Although 2f. domestica is unable to act as a carrier of patho- 

 genic micro-organisms in a manner similar to that of the mosquito, 

 so far as we know at present, nevertheless its habits render it a 

 very potent factor in the dissemination of disease by the mechanical 

 transference of the disease germs. These habits are the constant 

 frequenting and liking for substances used by man for food on the 

 one hand and excremental products, purulent discharges, and 

 moist surfaces on the other. Should these last contain pathogenic 

 bacilli, the proboscis, body and legs of the fly are so densely 

 setaceous (see fig. 96) that a great opportunity occurs, with a 



Fig. 96. Tarsal joints of one of posterior pair of legs of Musai domestica. Lateral 

 aspect to show densely setaceous character. 



maximum amount of probability, for the transference of the 

 organisms from the infected material to either articles of food or 

 such moist places as the lips, eyes, etc. As I have already pointed 

 out (1907), M. domestica is unable to pierce the skin, as certain 

 persons have suggested. The structure of the proboscis will not 

 permit the slightest piercing or pricking action, which fact elimi- 

 nates such an inoculative method of infection. It is as a mechanical 

 carrier, briefly, that M. domestica, and such allies as F. canicularis. 



