(142) 



STRUCTURE, DEVELOPMENT, AND BIONOMICS OF HOUSE-FLY. 383 



Nuttall (1. c.) records a personal communication of Stiles, 

 who placed the larvse of Musca with female Ascaris lum- 

 bricoides, which they devoured together with the eggs 

 contained by the nematodes. The larvaa and adult flies con- 

 tained the eggs of the Ascaris, and as the weather at the 

 time of the experiment was very hot the Ascaris eggs 

 developed rapidly and were found in different stages of 

 development in the insect, thus proving, as Nuttall points 

 out, " that the latter may serve as disseminators of the 

 parasite." These experiments of Grassi aud Stiles show that 

 flies can act as carriers of the eggs of these parasitic worms, 

 and that man could be infected by the fly depositing its 

 excreta on his food, or being accidentally immersed in food 

 as flies frequently are. 



VII. THE DISSEMINATION OF PATHOGENIC ORGANISMS BY 



MUSCA DOMESTICA AND ITS NON-BLOOD-SUCKING ALLIES. 



Although M. domestica is unable to act as a carrier of 

 pathogenic 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 excre- 

 rnental 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. 20) that a great opportunity occurs, with a 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 pro- 

 boscis will not permit the slightest piercing or pricking 

 action, which fact eliminates such an inoculative method of 

 infection. It is as a mechanical carrier, briefly, that M. 



