Page:Popular Science Monthly Volume 85.djvu/19

Rh fever, named from its supposed resemblance to typhus, and in olden times a malady of comparatively less importance, remains one of our grave sanitary problems.

The only household pest which still generally persists in city and country alike is the house-fly; and the public agitation against this insect has grown to such proportions in recent years that we may now look for substantial progress toward its elimination. The fly breeds in horse manure and other deposits of decomposing matter and it is always a carrier of filth, though only incidentally of disease. In paved and sewered cities there is little evidence that the fly is an important factor in disease transmission, but where human excreta are exposed, as in rural districts or cities with badly constructed privy vaults, the opportunity for flies to pick up the germs of typhoid fever and other diseases and carry them to food is so great that the danger becomes serious, particularly of course in the warm climates of our Southern States. During the Spanish War 142 out of every 1,000 of the men in our army camps contracted typhoid fever, and 15 out of every 1,000 died of it; and it was shown that the incidence of the disease was due mainly to careless disposal of excreta and consequent facilities for fly transmission. In Jacksonville, Fla., Richmond, Va., and other southern cities remarkable results in the reduction of typhoid and intestinal diseases have been attained by proper disposal of excreta and anti-fly campaigns. It is by no means a simple matter to control the multiplication of house-flies, but everything possible should be done, by trapping and by the cleaning up of possible breeding places, to reduce their numbers.

The transmission of typhoid fever by insects is, of course, only occasional and incidental, and even plague may at times assume a form in which it is spread directly from man to man by the discharges from the mouth. There is another class of diseases which are carried always and necessarily by insects, the germ passing through certain stages of its life history in man and others in the body of a particular insect host. The most important example in temperate climates is malaria. "Malaria," the bad air disease, was known to be somehow connected with night exhalations from swampy land and a large amount of curiously puzzling information about its prevalence was explained, only when it was shown fifteen years ago that it is transmitted by the bite of a particular mosquito which breeds in swampy pools and along the weed-grown margin of streams. It then became clear that marshlands did indeed cause malaria because their stagnant waters propagated the mosquitoes which carried the malaria germ from man to man. Malaria followed the turning up of the soil, not because emanations were set free in the process, but because digging produces pools of water which breed the insect hosts of the malarial microbe. The practical control of mosquitoes and the consequent elimination of malaria has been