THE HOUSE FLY 37 



of each host the parasite undergoes a certain development which is 

 essential to complete the life cycle and insure the perpetuation of the 

 malarial organism. Another kind of mosquito, in the tropics, is re- 

 sponsible in a similar manner for infecting human beings with yellow 

 fever. 



With these brief introductory remarks, we will now take up a dis- 

 cussion of the house fly and such other insects as are known to carry 

 disease germs. 



The House Fly, Musca domestica 



The common house fly has been associated with typhoid epidemics 

 so frequently during the past few years that Dr. Howard suggests that 

 it be called the " typhoid fly." 2 Even before the role of this insect 

 was definitely understood, it was suspected to have a connection with 

 the disease, because typhoid fever is generally most prevalent in late 

 summer, at the time when flies are the most abundant. I do not wish 

 to convey the impression that typhoid is spread only by means of flies, 

 for such is not the case. There are plenty of other agencies, such as a 

 polluted water or milk supply, but flies play a much more important 

 part in this connection than was supposed a few years ago, and the 

 house fly is more important than other species 'because of its great abun- 

 dance and its habit of occupying the dwellings of man and crawling 

 over his food. 



It was an old idea that flies were not only innocuous but were a 

 benefit to mankind. It is said that Sir John Lubbock provoked a 

 laugh in the House of Commons in 1873 by quoting as follows from 

 one of the books used in the elementary schools : " The fly keeps the 

 warm air pure and wholesome by its swift and zigzag flight." 3 



On the other hand, Kircher, 4 writing in 1658, makes the following 

 statement : " There can be no doubt that flies feed on the internal secre- 

 tions of the diseased and dying, then flying away, they deposit their 

 excretions on the food in the neighboring dwellings, and persons who 

 eat it are thus infected." 



As it took 240 years to demonstrate the truth of this theory, and 

 as twelve years have now passed, and the lesson of the Spanish war has 

 not yet come into general practise, it is a mooted question if, after all, 

 our progress is not an idle boast. At the present day there are many 

 persons who regard flies as a necessary nuisance, but who are not 

 awake to the dangers of their abundance. 



As a rule flies do not go far from their breeding places, and if they 

 are very abundant in any locality it is reasonably certain that their 

 breeding place is close at hand. 



2 L. O. Howard, Bureau of Entomology, Bull. 78, p. 23. 



3 G. H. F. Nuttall, Johns Hopkins Hospital Reports, Vol. VIII., p. 37. 

 * W. A. Riley, Science, February 18, 1910. 



