(C. R. Crosby)

The typhoid fly, or house-fly (Musca domestica).

For ages this ubiquitous pest has been looked upon as a harmless though annoying and unpleasant nuisance, and its presence has been tolerated as a necessary evil. It has now- been scientifically demonstrated that it plays an important role in the transmission of certain intestinal diseases, such as typhoid, cholera, infantile diarrhoea, etc., by carrying infected matter from the excreta of patients to the food of healthy persons. It is now thought that next after polluted water and contaminated milk, flies are the most important factor in the spread of typhoid. Both in city and in country the presence of these pests is a constant menace to the health of the community.

House-flies breed chiefly in horse manure, and to a less extent in garbage, human excrement, and other filth. Each female lays about 120 eggs, which hatch in a few hours. The maggots become full grown in about five days, and an equal period is spent in the pupal stage. The whole life cycle thus requires only ten to fourteen days in midsummer. In the climate of Washington, D.C., there are twelve or thirteen generations annually. Dr. L. 0. Howard reports finding 1200 larvae and pupae in a single pound of horse manure. The winter is passed either as adults hidden away in houses or as pupae beneath manure piles.

Control.

The house-fly nuisance can be abated most easily by the elimination of possible breeding-places. The great majority of the flies found in houses breed in piles of horse manure about near-by stables. Breeding in such places may be easily prevented by storing the manure, pending its removal, in a dark, fly-proof bin. This receptacle may be built as a lean-to attached to the stable with which it is connected by a small screen door. A larger door outside provides for the removal of the contents. The manure should be carted away at least once a week, and spread out on the land, where by drying it soon becomes unfit for breeding purposes. Whenever it is necessary to store such material in piles in the open, they should be located as far as possible from the nearest dwelling or milk-house. Flies do not usually travel more than one-fourth mile from the place in which they breed.

When only two or three horses are kept in a town, the manure can be handled in regular garbage-cans, in the same way as the kitchen refuse or ashes.

It is rather difficult to treat manure piles with any substance to prevent breeding: chloride of lime, kerosene, and iron sulfate have been tried, but when used in economical quantities are not effective.

Kitchen refuse and similar garbage should be kept in tight cans and removed at frequent intervals. Flies should be rigidly excluded from all places where food is exposed to contamination, including kitchens, dining-rooms, stores, etc. Especial care should be taken to protect milk and milk utensils, since milk furnishes an excellent medium for the growth of typhoid bacteria and is a common source of infection.

Flies may be driven from rooms by leaving one door open and darkening all the rest. Then evaporate a spoonful of carbolic acid over a lamp, or burn some pyrethrum insect-powder. They may be caught on sticky sheets, or poisoned with a sweetened 5 per cent solution of commerical formaldehyde.

On isolated farms each owner has it in his power by proper measures in the disposal of manure to reduce the fly nuisance to a minimum. In towns the case is different; there cooperation is necessary.

In attempting to reduce the numbers of house-flies in the District of Columbia, the health department has formulated a series of rules which L. O. Howard has summarized as follows: —

" All stalls in which animals are kept shall have the surface of the ground covered with a water-tight floor. Every person occupying a building where domestic animals are kept shall maintain, in connection therewith, a bin or pit for the reception of manure, and, pending the removal from the premises of the manure from the animal or animals, shall place such manure in said bin or pit. This bin shall be so constructed as to exclude rain water, and shall in all other respects be watertight, except as it may be connected with the public sewer. It shall be provided with a suitable cover, and constructed so as to prevent the ingress and egress of flies. No person owning a stable shall keep any manure or permit any manure to be kept in or upon any portion of the premises other than the bin or pit described, nor shall he allow any such bin or pit to be overfilled or needlessly uncovered. Horse manure may be kept tightly rammed into well-covered barrels for the purpose of removal in such barrels. Every person keeping manure in any of the more densely populated parts of the District shall cause all such manure to be removed from the premises at least twice every week between June 1 and October 31, and at least once every week between November 1 and May 31 of the following year. No person shall remove or transport any manure over any public highway in any of the more densely populated parts of the District, except in a tight vehicle which, if not inclosed, must be effectually covered with canvas, so as to prevent the manure from being dropped. No person shall deposit manure removed from the bins or pits within any of the more densely populated parts of the District without a permit from the health officer. Any person violating any of the provisions shall, upon conviction thereof, be punished by a fine not more than $40 for each offense."