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Page:Popular Science Monthly Volume 81.djvu/44

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38
THE POPULAR SCIENCE MONTHLY

The house fly does not bite, but its mouth parts are fitted for lapping and sucking up liquids. Another fly (Stomoxys calcitrans), called the stable fly, pierces the skin, and as this fly resembles the house fly and sometimes enters houses, many persons are mistaken in thinking that the house fly actually bites.

Breeding in filth and visiting all sorts of foul waste and decaying animal and vegetable matter and crawling over it, flies can not help becoming contaminated. At the first opportunity they will also crawl over food in the kitchen and drink from the milk pitcher. In this way some of the germs are rubbed off and adhere to the food and are swallowed with it by human beings. The diseases most commonly disseminated in this manner are those of the alimentary canal known as enteric diseases, such as typhoid fever, cholera and dysentery, the germs of which are voided in fecal matter, which if left exposed is certain to be visited by hundreds of flies, and some of the causative bacterial germs of these diseases are thus transferred to food, and infection is thus made possible. But it is not these diseases alone that may be and are occasionally carried by flies. There is considerable evidence to show that the house fly and its near relatives may carry the anthrax bacillus an their digestive systems and deposit the germs with their excretions, or may carry these germs exteriorly if the flies have visited foul matter "containing them. They may then infect persons by crawling over wounds or even food. Flies may carry the germs of tuberculosis by "visiting sputum and then crawling over the mouth and nose and food of persons. Kuttall made some interesting experiments in 1897 which proved that house flies not only may carry the germs of bubonic plague, commonly carried by fleas, but that they may actually die of the disease.[1]

It has been shown that the causative germs of some of these diseases may be and are taken into the digestive tract of the house fly and deposited upon food, confections or other substances. Thus the tiny fly specks which are the bane of every good housekeeper may be positively dangerous.

Formerly it was supposed that the house fly bred only in manure from the stables, and that it did breed in such places was pointed out as early as 1831 by Bouche. In 1873 Packard, and in 1880 Taschenberg, published accounts of the house fly showing that it usually breeds in horse manure. Packard records fourteen days as the period required to develop a generation. Dr. Howard in 1895[2] studied the insect, and had some difficulty in rearing it in captivity. The female laid 120 eggs, which hatched in eight hours, and the maggots lived five days before transforming. The pupa or cocoon stage also lasted five

  1. G. H. F. Nuttall, Johns Hopkins Hospital Reports, Vol. VIII., p. 16.
  2. L. O. Howard, Bureau of Entomology, Bull. 4, p. 46, 1896.