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 disease in 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 comimmis, 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 in large 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 Mvere 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 

 incul)ate at 37" C. for two days. 



