Periods. 
Cases. 
May 16 to 31, complete 
June 1 to 15, complete 
June 16 to 30, complete 
July 1 to 15, complete 
July 16 to 31, complete 
August 1 to 15, complete 
August 16 to 31, complete 
September 1 to 15, complete- 
September 16 to 30, complete. 
October 1 to 15, ineomplete_- 
October 16 to 31, incomplete-. 
1907. I 1906. 
12 1 
15 
32 
27 ' 
32 
39 ' 
101 
63 
131 
99 j 
139 
67 
70 
54 
59 
54 ! 
41 
«52 j 
98 
“17 
22 
“ Completed figures for October, including cases reported subsequent to November 1, 
are : October 1 to 15, 64 ; October 16 to 31, 42. 
The rate began to increase in the latter half of June and gTaduall}^ 
rose through July and the early part of August, reaching its maxi- 
mum about the middle of xVugust and then rather gradually declined 
through the latter half of August and through September. A com- 
parison of the rates for the summers of 1906 and 1907 shows that in 
1907 the increase in the rate was somewhat later, decidedly less, and 
with a rise and fall more gradual than that of 1906. (See Charts 
Xos. 1 and 2.) The total number of cases occurring in June, July, 
and August, 1907, was 310, while the total for the corresponding 
period of 1906 was 505, a difference of 195 cases. During the winter, 
spring, and fall seasons the rate of prevalence for the two years was 
about the same. (See Table, p. 23.) 
The results of our investigations suggest that the lower rate for 
the sunnner of 1907 for the most part was not due to a decrease in the 
operation of two known factors in the spread of typhoid fever infec- 
tion, viz, milk and contact. Of the 505 cases in the summer months 
of 1906 there were J8, or 9.5 per cent, that occurred in the course of 
two pronounced milk outbreaks, and were attributed to infected milk. 
Of the 310 cases in the corresponding period of 1907, 28, or 9.03 per 
cent, occurred in the course of a pronounced milk outbreak and were 
attidbuted to milk infection. 
Of the 7d7 cases investigated by us and considered as having con- 
tracted the infection in the District of Columbia in 1906, 7.3 per cent 
were fairly definitely attributable to infection by direct or indirect 
contact; while of the 523 cases in 1907, 19 per cent were fairly defi- 
nitely attributable to infection by direct or indirect contact. Thus, so 
far as the results of our investigation indicate, milk as a factor in pro- 
nounced outbi’eaks operated relatively to about the same extent 
during the two summers and contact operated as a factor relatively 
to certainly as great an extent in the 1907 period as it did in the 1906 
