MOSQUITOES. HOUSE-FLIES 249 



prevalence of the disease, and will prevent the occurrence of new 

 malarial infections. 



It must be remembered that when a person is once infected, the 

 organisms may remain in the body for many years, producing from 

 time to time relapses of the fever. 



A case of malarial infection in a house (whether the person is 

 actively ill or the infection is latent) in a locality where anopheles 

 mosquitoes are present, is a constant source of danger, not only to 

 the inmates of the house, but to the immediate neighborhood, if 

 proper precautions are not taken. It should be noted in this 

 connection that the mosquitoes may remain in a house through an 

 entire winter, and probably infect the inmates in the spring upon 

 the return of the warm weather. 



The House-Fly (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 demon- 

 strated 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. 



