278 
TYPHOID FEVER IX DISTRICT OF COLUMBIA. 
cited bv Mason^ the '‘danger signal'’ of the pollution of this partic- 
idar well under discussion was first discovered, not in the findings of 
the chemical analysis, as held by Mason, but in the occurrence of 
disease in this particular residence and in the fact that on these 
premises a “ dry-steyned " cesspool and a shallow well were "both 
sunk in gravel" at the short distance of only 4 yards apart. While 
it is well to bear in mind the present unsettled condition of opinion 
which prevails on the subject of sanitary water analysis and which in 
itself is no new thing, it is not a part of the problem before us to 
enter into any discussion of these conflicting views, but simply to 
make such use as we can of chemical analysis as one of the several 
means to the end of arriving at the cause of typhoid fever in the 
District of Columbia. 
Our present inquiry, therefore, has included the chemical examina- 
tion or sanitary analysis of the principal kinds of water used for 
drinking pimposes in the District of Columbia. Broadly, the several 
kinds of water used for drinking pimposes in this locality niay be 
classified as follows ; 
First, the filtered water of the Potomac River, which is used for 
drinking pimposes by certainly the gi’eater number of the inhabitants 
of W ash in gt on and the District of Columbia ; secondly, the waters of 24 
deep and 63 shallow public wells, distributed over a comparatively 
large area, but located in largest number in the northwest portion of 
the city, the waters of which are used for drinking purposes by a con- 
siderable number of persons: and thirdly, a number of so-called 
table or bottled waters, including distilled water, manufactimed here 
and elsewhere, and of which a considerable number are used for 
drinking purposes among the wealthier classes, but which obviously 
are used by a fewer number of persons. Oiu study has also included 
the chemical examination of the local water supplies of certain insti- 
tutions and communities, such as that of the Government Hospital 
for the Insane, Soldiers' Home, and Chevy Chase. IVe have also 
examined a number of samples of ice, sold and manufactured in the 
city, and a mmiber of wells used in connection with ice plants, either 
for the manufactme of ice or for the purposes of mechanical cooling 
and condensation, ot’ both. 
METHODS OF ANALYSIS. 
So far as practicable, we have followed the standard methods of 
water analysis recommended by the committee on standard methods 
of water analysis of the American Public Health Association, which 
are set forth in detail in their final report published in Supplement 
Xo. 1, May, 1905, of the Journal of Infectious Diseases. Our exami- 
nation included, in most instances at least, the determination of 
total solids, chlorine, free and albuminoid ammonia, nitrites, nitrates, 
