Page:Popular Science Monthly Volume 58.djvu/263

Rh striking. At the Presidio camp, the chance for the transfer of typhoid by flies had by intelligent care been reduced to zero. This, however, Mas, of course, a more or less permanent camp and opportunities were better, but indicated in a beautiful way what might be done and what should be done even in a temporary camp.

(2) In towns where the box privy nuisance is still in existence the house-fly is attracted to such places to a certain extent, though not as abundantly as other flies, which, however, are not found in houses. Observations to this effect were made by the writer and his assistants in many parts of the United States.

(3.) In the filthy regions of a city, where sanitary supervision is lax, and where in low alleys and corners and vacant lots deposits are made by dirty people, the house-fly is attracted to the stools, may breed in them, and is thus a constant source of danger. The writer has seen a deposit made over night in South Washington in an alleyway swarming

with flies, in the bright sunlight of a June morning, temperature 92° F., and within thirty feet of this substance were the open doors and windows of the kitchens of two houses occupied by poor people, these two houses being only elements in a long row.

The conclusions which the writer has reached after two years of this experimental work are:

(1) Of the seventy-seven species of flies found under such conditions that their bodies, especially their feet and their proboscides, may become covered with virulent typhoid germs, only eight are likely to carry them to objects from which they can enter the alimentary canal of man.

(2) Of these eight species, two, namely, Lucilia cæsar and Calliphora erythrocephala. can very rarely carry such germs, though they may carry the germs of putrefaction and cause blood-poisoning, in alighting upon abrasions of the skin or open wounds.