31 
It ^vill be observed that the flies were at their maximum abundance 
about July 1. The number from that time diminished fairly uni- 
formly from week to week until August 5, when the average number 
caught was only about one-half as much as the average on July 1. 
The number rose for the week ended August 12, and then continued 
to fall through the remainder of August and the greater part of 
September. A rise in the curve is noted for the two weeks ended 
October 21. 
The typhoid fever curve (see Chart No. 1) reached its maximum 
about July 1 and continued along at about the same height imtil 
about the 10th of September, when a decline began which continued 
fairly uniform until the latter part of September. The rise in the 
curve in the latter part of September and the early part of October 
was due largely to a milk outbreak (see p. 102). 
Chart No. 7, prepared by us, shows the fly abundance and the 
number of cases of typhoid fever in periods of two weeks. In this 
chart the cases of typhoid fever attributed to milk infection and to 
direct contact with previous cases are eliminated, only the cases due 
to causes undetermined being counted. By lengthening the periods 
many of the sharp turns in the curves as presented on charts Nos. 5 
and 6 are removed and the relation of the curves can be followed with 
better understanding. 
As the cases are charted by date of definite onset, probably about 
three weeks subsequent to the time of infection for the majority of 
the cases, the curve for the abundance of flies, if moved forward three 
weeks, should parallel the curve of prevalence of typhoid fever, pro- 
vided a relation of cause and effect existed. If this is done, the 
parallelism certainly is not sufficiently striking to warrant the con- 
clusion that flies play much of a role in the transmission of typhoid 
fever in Washington. 
The chances of dissemination of infection by flies in a well-sewered 
city of course are much less than in a camp when proper care is not 
taken in the disposal of excreta. It is difficult to estimate what part 
flies play in the spread of the disease in W ashington, but the evidence 
is quite strong that it is relatively a small part. That flies are a 
minor factor for the city as a whole does not preclude the possibility 
that in certain limited localities they from time to time may spread 
the infection. Therefore, in carrying out preventive measures against 
typhoid fever, the number of flies should be lessened by a proper 
control of their breeding places, and their access to infectious matter 
and food stuffs prevented. 
