CHEMICAL EXAMINATION OF THE WATER SUPPLY OF THE 
DISTRICT OF COLUMBIA. 
It must certainly be admitted in the light of our present knowledge 
that, as a general thing, the cause or causes of typhoid fever in any 
community lie beyond the reach of chemical investigation. Indeed, 
it is doubtful whether in all instances the more remote causes of the 
disease are even within the immediate scope of bacteriology, for the 
reason that ovdng to the time which must necessaril}’- elapse between 
the recognition of the disease in the individual and the time of infec- 
tion the immediate source of the infection mav have ceased to exist, 
so that we are of the opinion, so ably advanced by Professor Sedg- 
wick,® that it frequently happens that the cause or causes of such 
diseases as typhoid which have become endemic are to be sought for, 
not only in the laboratory, but in the community at large, through 
the study and comparison of sanitary statistics, which, in many 
cases at least, represent results and data covering long periods of 
time. 
On the other hand, it occasionally^ happens, as recently pointed 
out by Professor Mason, ^ that in some instances at least, notably in 
the case of certain well waters, the danger signal of a serious condition 
of pollution has been held out by the chemical side of the investiga- 
tion alone, and while, as he puts it, bacteriology deals with the pres- 
ent, chemistry, in the case of a natural water, deals with the past, and 
may occasionally, at least, throw some light on the future in so far 
as pollution or infection is concerned. 
It should be borne in mind, however, that among others who 
have done a very great amount of work in this field, and whose 
opinions are in every way entitled to respect, there are some who are 
inclined to question the value of a sanitary water analysis, and, as 
has recently been pointed out by Leighton‘S in criticism of the case 
“ See address delivered before Section K of the American Association for the 
Advancement of Science, Xew Orleans, December, 1905. Science, New Series, Vol. 
XXIII, No. 584, pp. 362-367. 
^ “Interpretation of a Water Examination,” by W. P. Mason. Science, New Series, 
Vol. XXI, No. 539, pp. 644-653. 
cSee “The Futility of a Sanitary Water Analysis as a Test of Potability,” by Mar- 
shall 0. Leighton, in Biological Studies by the Pupils of William Thompson Sedgwick, 
Boston, 1906, pp. 36-53. 
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