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 
stud)'’ 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. 
