STRUCTURE, DEVELOPMENT, AND BIONOMICS OF HOUSE-ELY. 383 
Nuttall (1. c.) records a personal communication of Stiles, 
wLo placed the larvte of Musca with female Ascaris lum- 
bricoides, which they devoured together with the eggs 
contained by the nematodes. The larvae and adult flies con- 
tained the eggs of the Ascaris, and as the weatber at the 
time of the experiment was very hot the Ascaris eggs 
developed rapidly and were found in diiferent stages of 
development in the insect, thus proving, as Xuttall points 
out, “ that the latter may serve as disseminators of the 
parasite.” These experiments of Grassi and 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 op Pathogenic Organisms by 
31 USCA DOMES TIC A AND ITS NON-BlOOD-SUCKING AlLIES. 
Although 31. 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- 
meutal 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 flg. 20) that a great opportunity occurs, with a maximum 
amouut 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), 31. 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 31. 
