140 THE HOUSE FLY— DISEASE CARRIER 



they have discovered the origin of a typhoid epidemic 

 if they observe a few piles of horse manure in the 

 alleys of a city take a wide leap over logical difficulties. 

 Their mode of reasoning seems to be this: Flies can 

 breed in horse dung, flies can convey typhoid fever, 

 therefore flies bred in these dung heaps have caused or 

 are about to cause typhoid fever. One other essential 

 condition, namely, the existence of infected material 

 to which the flies have access, is left out of account in 

 such hasty judgments. 



"As a matter of fact, grave as is the danger of fly 

 transmission of typhoid under rural conditions, it does 

 not seem to be an important factor in the production 

 of urban typhoid. As is well known, the intensive 

 study of typhoid fever in Washington, D. C, which 

 extended over several years, yielded no evidence that 

 fly transmission had any noteworthy share in typhoid 

 fever causation in that city. 



"One of the most experienced American health of- 

 ficers has taken a decided stand on this question in a 

 book recently published.* While recognizing the de- 

 sirability of treating garbage in such a way as to pre- 

 vent a nuisance, and admitting the possibility of fly- 

 borne infection where open privy vaults exist, he de- 

 clares very plainly that 'there is no evidence that in 

 the average city the house fly is a factor of great mo- 

 ment in the dissemination of disease.' There can be 

 no doubt that in any reasonably clean and well- 



*Chapin, Charles V. : Sources and Modes of Infection. New 

 York. 1910. 



