The body of the house fly is covered thickly with hairs and bristles of
varying lengths, and this is especially true of the legs. Thus, when it
crawls over infected material it readily becomes loaded with germs, and
subsequent visits to human foods result in their contamination. Even
more dangerous than the transference of germs on the legs and body of
the fly is the fact that bacteria are found in greater numbers and live
longer in its alimentary canal. These germs are voided, not only in the
excrement of the fly, but also in small droplets of regurgitated matter
which have been called "vomit spots." When we realize that flies
frequent and feed upon the most filthy substances (it may be the excreta
of typhoid or dysentery patients or the discharges of one suffering from
tuberculosis), and that subsequently they may contaminate human foods
with their feet or excreta or vomit spots, the necessity and importance
of house-fly control is clear.
In army camps, in mining camps, and in great public works, where large
numbers of men are brought together for a longer or shorter time, there
is seldom the proper care of excreta, and the carriage of typhoid germs
from the latrines and privies to food by flies is common and often
results in epidemics of typhoid fever.
And such carriage of typhoid is by no means confined to great temporary
camps. In farmhouses in small communities, and even in badly cared for
portions of large cities, typhoid germs are carried from excrement to
food by flies, and the proper supervision and treatment of the breeding
places of the house fly become most important elements in the prevention
of typhoid.
In the same way other intestinal germ diseases, such as Asiatic cholera,
dysentery, enteritis (inflammation of the intestine), and infantile
diarrhea, are all so carried. There is strong circumstantial evidence
also that tuberculosis, anthrax, yaws, ophthalmia, smallpox, tropical
sore, and the eggs of parasitic worms may be and are carried in this
way. In the case of over 30 different disease organisms and parasitic
worms, actual laboratory proof exists, and where lacking is replaced by
circumstantial evidence amounting almost to certainty.