124 THE HOUSE FLY—DISEASE CARRIER 
in contaminated water and by infected flies dropping 
into it. 
When it comes to butter and cheese, however, we 
have long-lived foods, and the possibilities of their con¬ 
tamination by flies and their subsequent use is of espe¬ 
cial interest, and more particularly as to the length of 
time that they will harbor virulent germs gained in this 
way or in any other. 
Dr. John R. Mohler, of the Bureau of Animal In¬ 
dustry of the United States Department of Agriculture, 
informs the writer that investigations made in his of¬ 
fice show that typhoid bacilli will live in butter under 
common market conditions for 151 days, and still be 
able to grow when transferred to suitable conditions. 
In milk under market conditions they retain active mo¬ 
tility for twenty days, after which time there is a lessen¬ 
ing in numbers until on the forty-third day of the test 
they disappear from view. At certain seasons of the 
year large numbers of flies collect upon the vats in 
which milk and cream are being stored in dairies and 
creameries; many flies fall in, their bodies being 
strained out when the cream is sent to the churn. If 
any of these flies carry typhoid bacilli these are washed 
off by the milk and remain in the butter or cheese made 
from it. Thus the eating of butter contaminated in 
this way may account for very many cases of typhoid 
fever the cause of which cannot otherwise be traced. 
