Bacteriological Examination. 181 



The presumptive tests for Bacillus coli showed that gas- 

 producing organisms were present in a majority of i-c.c. 

 samples, and typical colon bacilli were isolated. In this 

 case the contamination was brought about by cattle gam- 

 ing access to the area immediately surrounding the spring; 

 but the same conditions might easily have led to infec- 

 tion from human beings. 



Similar results have been reported by Savage and 

 Bulstrode (Savage, 1906) in the examination of the water- 

 supply of Bridgend. 



It seems to the writers that the real application of 

 chemistry begins where that of bacteriology ends. When 

 pollution is so gross that its existence is obvious and only 

 its amount needs to be determined, the bacteriological 

 tests will not serve, on account of their excessive delicacy. 

 In studying the heavy pollution of small streams, the 

 treatment of trades wastes, and the purification of sewage, 

 the relations of nitrogenous compounds and of oxygen 

 compounds are of prime importance. In other words, 

 when pollution is to be avoided, because the decompo- 

 sition of chemical substances causes a nuisance, it must 

 be studied by chemical methods. When the danger is 

 sanitary and comes only from the presence of bacteria, 

 bacteriological methods furnish the best index of pollution. 



In the study of certain special problems the paramount 

 importance of bacteriology is generally recognized. The 

 distribution of sewage in large bodies of water into which 

 it has been discharged may thus best be traced on account 



