Page:Popular Science Monthly Volume 76.djvu/220

216 disease; and the studies made on insects, by physicians, have been as important as those made on the afflicted patient.

The identification of a species of Glossina or tsetse fly as an agent in the spread and transmission of the "sleeping sickness" is one of the more recent accomplishments in this direction, and opens a way for dealing with this plague that has practically depopulated great areas in Africa.

This seems like a series of heavy indictments against a lot of insignificant creatures whom, heretofore, we have deemed ourselves justified in ignoring. But the case has been understated rather than otherwise, and it is time that we recognized insects as among the most dangerous enemies to man from the sanitary standpoint.

Let me put it in a somewhat different way: could we at a blow eliminate all the members of the single order Diptera—including the fleas—we should at the same time absolutely eliminate malaria, yellow fever, dengue, jungle and several other kinds of tropical fevers, the bubonic plague, sleeping sickness, filariasis, several forms of eye diseases certain ulcerating sores in tropical countries, and we should reduce to a minimum enteric fevers of all kinds, lessen the death rate from tuberculosis and pulmonary troubles, and probably modify or lessen leprosy and kindred diseases.

But this is not all our plaint; for besides attacking man directly in his bodily health and comfort, they attack his domestic and other animals and lessen their value if they do not absolutely destroy them.

Every one of our domestic animals and all our feathered friends of the barnyard are infested by lice—biting and sucking and some of them harbor several species. All of them are well adapted in form to the conditions under which they live; and even the hog, which is not usually thought of as a hairy animal, has a species that manages to move about as freely as need be among the bristles. Naturally, animals so infested can not do their best for their masters; they become mangy in appearance, do not grow well, the fowls lessen in egg production and the cows in milk.

To the dairyman, flies—comprehensively speaking—are nuisances from all points of view. In the pasture Tabanids in great variety get after them; in the stable Stomoxys is always on hand. Occasionally the fauna of one country contributes a pest to that of another, as was the case when the so-called horn-fly was introduced about twenty years