146 THE HOUSE FLY—DISEASE CARRIER 
Sykes’s observations in his own home city, but never¬ 
theless Doctor Chapin is a well-known man of high 
scientific standing and his conclusions must be viewed 
with all respect. When we come to analyze the situa¬ 
tion, however, it becomes at once apparent that in cities 
the correlation or non-correlation of the curve of house 
fly abundance and of the abundance of typhoid has 
practically no effect upon our conclusions as regards 
the possible transfer of the disease by flies. 
Flies are numerous at all times during the summer, 
and wherever excreta carrying virulent germs can be 
reached by them it is sure to be covered by them— 
whether in early June or in October—and the chances 
are almost as great that food supplies will be reached 
by these flies whether there are 500 of them or 600 of 
them. The fact that typhoid fever does not develop 
in localities where flies are most numerous does not 
mean that it is not carried by flies, but simply means 
that the flies in that locality have had no opportunity 
to visit substances containing virulent germs. A cor¬ 
relation of the two curves in question has been found 
by Doctor Jackson in his report to the Merchants’ As¬ 
sociation of New York, and it has been found by Cap¬ 
tain Ainsworth in his studies of the house fly and 
enteric fever in India, by Purdy (1910) in New 
Zealand, and by Osmond (1909) in Cincinnati, and 
where it is coincident it may serve to attract the atten¬ 
tion of people to the subject, but the absence of the 
correlation in any given case is a most inconclusive ar¬ 
gument. 
