CHAPTER XXXV. 



THE BACTERIOLOGICAL EXAMINATION OF WATER, AIR, AND 



SOIL THE CONTAMINATION AND PURIFICATION OF 



WATER THE DISPOSAL OF SEWAGE. 



THE bacteriological examination of water is undertaken with the 

 purpose of discovering whether any pathogenic bacteria are liable 

 to be present. The determination of the number of bacteria in water 

 was for a time considered of great importance, then it fell into disrepute, 

 and the attempt was made to isolate the specific germs of diseases which 

 were thought to be water-borne. At first these attempts seemed very 

 successful in that supposed typhoid bacilli and cholera spirilla were 

 found. Further study revealed that there were common water and 

 intestinal bacteria which were so closely allied to the above forms 

 that the tests applied did not separate them. Even the use of a serum 

 from an animal immunized to injections of the typhoid bacillus was 

 found to agglutinate some other bacteria in high dilutions; so that the 

 test as usually carried out was insufficient. With the latest technique 

 it is probable that the serum from an immunized animal from which 

 the group agglutinins have been absorbed will be sufficient to identify 

 any bacillus which it agglutinates. The practical impossibility of get- 

 ting typhoid bacilli from suspected water caused a return to the esti- 

 mation of the number of bacteria in water and above all to the estima- 

 tion of the number of intestinal bacteria. It is known that the group 

 of colon bacilli have about the same duration of life as the typhoid 

 bacilli, and as the colon bacilli come chiefly or wholly from the intes- 

 tinal passages of men and animals, it was fair to assume that typhoid 

 bacilli could not occur without the- presence of the colon bacillus. The 

 latter could, of course, occur abundantly without the typhoid bacillus. 



During the past few years the attention of sanitarians has peen seri- 

 ously devoted to the interpretation of the presence of smaller or larger 

 numbers of colon bacilli in water, until at present upon the quantitative 

 analysis (measuring, within certain limits, decomposing organic matter) 

 and the colon test (indicating more specifically that derived from intes- 

 tinal discharges; the bacteriological analysis of water is based. 



Technique of Quantitative Analysis. The utmost care is necessary 

 to get reliable results. A speck of dust, a contaminated dish, a delay 

 of a few hours, an improperly prepared ji<rar or uvlatin, a too high or 

 too low temperature, may introduce an error which would make a 

 reliable test impossible. 



COLLECTION OF SAMPLES. The small sample taken must represent 

 the whole from which it was drawn. If a brook-water, it must be taken 

 some distance from the bank; if from a tap, the water in the pipes must 



