EXAMINATION OF WATER. 439 



The detection of the typhoid fever and cholera bacilli 

 has been discussed in the preceding pages and need, there- 

 fore, receive no further attention at this place. In addition 

 to these organisms, the water may contain bacteria which 

 are highly pathogenic and these, consequently, deserve es- 

 pecial consideration. 



Pathogenic bacteria. The chief object of the bacterio- 

 logical examination of water is to determine the presence or 

 absence of pathogenic or toxicogenic bacteria. In the 

 method as ordinarily carried out, this is done by recogniz- 

 ing the colony of the specific organism sought for. When 

 the pathogenic bacteria, as the cholera or typhoid fever 

 bacillus for example, are present in large numbers, and this 

 is very rarely the case, the identification can perhaps be 

 easily done. On the other hand a few pathogenic bacteria 

 in the presence of a large number of saprophytic organisms 

 can be easily overlooked, and in such cases their recogni- 

 tion becomes well-nigh impossible. In view of these facts 

 the following method was devised by Vaughan, and has 

 been used in this laboratory since 1888. It is based upon 

 the fact that a large number of the bacteria present in 

 water are common saprophytes which grow at the ordinary 

 temperature, cannot grow at the temperature of the body, 

 and cannot, therefore, produce toxic or pathogenic effects. 

 The bacteria which can develop at the temperature of the 

 body may, or may not, be pathogenic. This can only be de- 

 cided by an animal experiment. The method employed is 

 as follows: 



By means of a sterile pipette 1 c.c., 0.5 c.c. and 1 drop 

 of the water are added, respectively, to each of three tubes, 

 pf bouillon. These are set aside in the incubator at 39 for 

 24 hours. If no growth occurs at this temperature it is at 

 once sufficient evidence that the water is free from disease- 

 producing organisms. On the other hand, if a growth does 

 develop, injections of 1 c.c. of the culture are made intra- 



