Practical preventive medicine . transmission of plague, and flies,principally the house fly, in the transmission of the others. Inthe case of the former, the plague bacillus leaves the fleasbody both by the probocis and the feces; in the case of the lattergroup, the flies probocis, its excreta, regurgitated material andthe exterior of its body surface may afford means of convey-ance. In the former instance the infective agents are directlyreintroduced by the insect into a new host, in the latter trans- INSECTS AS VECTORS OF INFECTIVE AGENTS l83 mission is effected through the contamination of
Practical preventive medicine . transmission of plague, and flies,principally the house fly, in the transmission of the others. Inthe case of the former, the plague bacillus leaves the fleasbody both by the probocis and the feces; in the case of the lattergroup, the flies probocis, its excreta, regurgitated material andthe exterior of its body surface may afford means of convey-ance. In the former instance the infective agents are directlyreintroduced by the insect into a new host, in the latter trans- INSECTS AS VECTORS OF INFECTIVE AGENTS l83 mission is effected through the contamination of food by theinsect. 3. The Activity of the House Fly.—The house fly (Muscadomestica) (Fig. 67) is an ubiquitous insect with a world widedistribution, living in close association with man. Its ova arepreferably deposited in manure piles, from these hatch thefamiliar maggots (Fig. 68), which burrow through the pileand feed on the decaying organic matter. In about a week inthe summer these leave the manure and burrow in the soil. Pig. 67.—The house fly. {Public Health Reports, Supplement 29.) where they pupate. In a few days the adult fly emerges. Theentire life cycle may be completed under favorable circum-stances in from 10 to 14 days. The dangers arising from thisinsect are due to its promiscuous feeding habits and its intimateassociation with man. It will walk over and feed upon thefecal deposits in a privy, the refuse in a garbage can, the pas-tries in a bake shop and the food in the kitchen and pantry withequal impartiality and in turn, conveying infective agentssecured from the excreta to food during its journey. There isabsolutely no question but that in unsewered cities and towns 184 PRACTICAL PREVENTIVE MEDICINE or in rural areas where fly tight privies are not used, flies are agreat menace and an actual source of danger. They are un-doubtedly a considerable factor in the autumnal increase intyphoid. A very marked reduction in the incidence of typhoidfever was secured
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Keywords: ., bookcentury1900, bookdecade1920, booksubjectprevent, bookyear1920
