Kirchner — Bacteriological Examination of River Water. 287 
of sewage pollution, and we may assume that the possibility 
of the presence of disease germs is greater. The numerical 
estimation is also useful in determining the mixture, dilution 
and current of a stream as influenced by sewage or tributaries. 
The Isolation of Pathogenic Bacteria. —In the examina- 
tion of water, our chief interest centers in the discovery and 
isolation of those organisms which cause diseasein man. We 
know that typhoid fever and cholera are often transmitted to 
man through the agency of drinking-water, and any tests 
that help in the identification of the bacteria which produce 
these diseases or which will lead us to suspect their presence 
are worthy of consideration. Since, in this country, typhoid 
fever is the more prevalent of the water-born diseases, it has 
received most attention. We know furthermore that sewage 
often contains disease-producing bacteria, and the study of 
sewage bacteria, and especially the isolation of B. coli com- 
munis, has been considered of great importance. 
The intestinal tract of man and animals has been regarded 
by some as the normal habitat for B. coli communis, and its 
presence in water has been taken as evidence of sewage pollu- 
tion. While this latter assertion is true in a measure, we 
should hesitate to make a positive statement regarding sewage 
pollution until we have proved by quantitative tests that 
B. coli communis is present inlarge numbers. We must, how- 
ever, first devise means for the isolation of this organism. 
In the routine examination of water where many samples 
are to be analyzed, it must be evident that the detailed 
methods of isolation and identification are too cumbersome to 
be of practical value, and we are compelled to resort to short 
methods which are considered ‘‘ presumptive tests.’’ Such 
tests for the identification of B. coli communis were used in 
our laboratory, and, inasmuch as our method gave excellent 
results, I will give it in outline. 
PRESUMPTIVE TESTS FOR B. COLI COMMUNIS. 
(1) Inoculate broth tubes to which 4 drops of Parietti 
solution have been added with 1.c.c. of sample of water and 
incubate at 37° C. for two days. 
