98 
Chart No. 10 shows the percentage of 10 c. c. samples of water 
from the filtered-water reservoir and various taps, giving the pre- 
sumptive test for B. coli (fermentation in lactose broth). 
It will be noted that the percentage of samples of water from the 
storage (filtered) water reservoir giving fermentation is considerably 
lower than that of the samples taken from the different taps. It is 
difficult to explain why this should be so. Two possible explana- 
tions present themselves. 
1. Contamination of the water in the mains by suction or seepage 
into the mains through loose joints, cracks, etc. This is distinctly a 
sanitary engineering problem. 
2. Continued life and perhaps multiplication in the mains of organ- 
isms capable of producing fermentation. 
THE RELATION OF TYPHOID FEVER TO POTOMAC RIVER WATER. 
In our first report upon typhoid fever in the District of Columbia 
in 1906 we lacked sufficient data to draw definite conclusions upon 
the relation of the Potomac Kiver water to the disease. In our 
second report (for 1907) we concluded that — ; 
The filtered Potomac River water during the typhoid season of 1907 (May to Sep- 
tember) was, according to present bacteriologic standards, of good sanitary quality 
and so far as could be ascertained was not responsible for the spread of the infection. 
In the typhoid season of 1907 there were about 200 cases less than in the 1906 period. 
This improvement in the situation suggests that the diminution of the amount of 
typhoid fever in the District of Columbia was due to the improvement in the quality 
of the drinking water as the result of sand filtration. Positive proof of this can not 
now be established. 
In the 1908 period the filtered water was found to be of about the 
same quality as it was in the 1907 period, and the rate of prevalence 
of typhoid fever in the 1908 period was about the same as it was in 
the 1907 period. 
The number of cases occurring in the District of Columbia in the four 
months June, July, August, and September, of the three years, was as 
follows: In 1906, 605 cases; in 1907, 418 cases; in 1908, 390 cases. 
The results of the bacteriological examination of the filtered water 
for periods of the three years were as follows: 
Date. 
Where taken. 
Number 
of 
samples. 
Average 
number 
of bac- 
teria per 
Percentage of 
samples showing 
B. coli— 
cubic cen- 
timeter. 
In 1 c. c. 
i 
In 10 c. c. 
1906. 
Per cent. 
Per cent. 
[ Storage reservoir 
13 
44 
7. 7 
15.4 
July 16 to August 31, inclusive 
[Tap 
60 
67 
3.3 
26.6 
1907. 
May 15 to August 31, inclusive 
Storage reservoir. . 
91 
31 
0 
2.2 
1908. 
May 1 to August 31, inclusive 
Storage reservoir 
90 
48 
1.1 
6.6 
