CHAPTER XI. 



BACTERIOLOGY OF WATER, AIR, AND SOIL. 



Bacteriological examination of water is of importance for the 

 determination of the presence of pathogenic bacteria, and for the 

 enumeration of the total number of all bacteria contained therein, 

 the latter being considered an index of the purity of the water. 



Several well known pathogenic bacteria have been found in water ; 

 among these are the typhoid, anthrax, cholera, plague, and colon 

 bacilli, also the pus cocci. Since the tetanus bacillus is a normal 

 inhabitant of the cultivated soil and manure, it is not at all uncom- 

 mon to find it, at times, in muddy waters. 



Bacteriological examinations of water are, in a measure, very 

 disappointing, because it is very difficult, and at times impossible 

 to determine the presence of the typhoid bacillus, even when it is 

 certain that it is present, having been added to water to be ex- 

 amined it is even then difficult to isolate. 



The fact that the colon bacillus is always found in water con- 

 taminated by feces is a great help in the recognition of polluted water. 

 In the case of typhoid contamination the typhoid bacillus may elude 

 detection, but the colon bacillus is easily found; we may then assume 

 that, since it is impossible for typhoid bacilli to reach water without 

 the colon bacilli that water having no colon bacilli is also free from 

 typhoid bacilli. Also water having colon bacilli in great numbers 

 is contaminated with feces, and perhaps typhoid feces. The detec- 

 tion of the colon bacillus is therefore of prime importance in the ex- 

 amination of drinking water. Its detection is simple. Water must 

 be collected in sterile bottles, using every precaution against acci- 

 dental contamination. Fermentation tubes are employed, contain- 



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