268 
TYPHOID FEVER TH DISTRICT OF COLUMBIA. 
contains a few more organisms (average 64 per cubic centimeter) 
than the effluent from the filters. 
Our data upon the number of bacteria found in the raw water is 
too limited to give the percentage reduction. Taking the figures of 
the filtration laboratory for the same period, viz, average 7,619 bac- 
teria per cubic centimeter in the raw water, we have 99.2 per cent 
removed by the entire water system. 
Our limited studies confirm the fact that a large number of bac- 
teria are eliminated in the storage and subsiding basins, as well as in 
the sand filters. 
As far as the colon bacillus is concerned, some of them pass the 
filters and survive in the water as it is collected in the filtered water 
reservoirs and as it runs from the taps. The number of samples of 
tap water containing the colon bacillus diminished from the last of 
July throughout the remaining period during which these tests were 
made (see p. 27). 
Fifteen and two-tenths per cent of the samples of tap water exam- 
ined contained the colon bacillus in 10 cc., 2.2 per cent in 1 cc., 
making a total of 17.5 per cent of the samples of tap water examined. 
The raw water, according to our studies, contained the colon 
bacillus in 71.7 per cent of the samples examined. Sixty-nine per 
cent of the raw water samples examined during the same period at 
the laboratory of the filtration plant contained the colon bacillus. 
This gives an approximate reduction of about 77 per cent of the 
colon bacilli in the river water by storage and filtration. 
THE MUD IN THE WATER PIPES. 
The suggestion has been advanced by some that the large amount 
of mud contained in the pipes of the water s^^stem retains the typhoid 
infection, this being distributed throughout the city. From our 
knowledge of the viability of the typhoid bacillus, we should think 
this to be unlikely, and a few experiments confirmed this opinion. 
Some of this mud was placed in ordinary 1-inch iron pipes, sterilized, 
and then abundantly planted with t}^phoid cultures. Two pipes 
thus prepared, containing the typhoid infected mud, were kept, one 
at room temperature and one at 15° C. It was found that the organ- 
isms were still alive at the end of thirty days but dead at the end 
of two months. 
THE BACTERIOLOGICAL STUDIES OF POTOMAC WATER IN 
PREVIOUS YEARS. 
It is interesting to compare these results with the work of others 
upon the bacterial content of Potomac water in previous }^ears. 
In 1897 and 1898 extensive analyses of the Potomac River water 
were made in the Hygienic Laboratory, United States Public Health 
