THE PREVENTION OF THE SPREAD OF DISEASE BY
RELATION OF HOUSE FLIES TO DISEASE.
From very early ages it has been suspected that flies were
instrumental in the spread of disease, but it was not until the
Spanish American War in 1898, and in the Boer War of 1900, that
they were proved, under certain conditions, to be the most important
factors in the dissemination of typhoid or enteric fever.
Flies may convey the organisms of disease in two ways. If a
fly has been in contact with infectious matter, some of it may be
carried away on its limbs, which are very hairy; or if it has been
feeding on such matter, the organisms of disease will be taken into
its digestive system, from which they will be discharged either by
regurgitation or defaecation. In most cases the infectious matter
which is carried by the fly is deposited in food, which thus becomes
contaminated and capable of infecting human beings. In one, or
both of these ways typhoid fever, or summer diarrhoea or even
tuberculosis may be spread.
There are other diseases which flies are believed at times to
convey from deceased to healthy persons; but the above-mentioned
are enough to justify the most extreme measures being adopted to
diminish their prevalence.
In order to understand how best to apply preventive measures,
it is necessary to consider briefly the life history of the fly.
LIFE HISTORY OF THE DOMESTIC FLIES.—Flies begin
breeding in the months of June and July, and continue to breed until