CHAPTER XI 

 BACTERIOLOGY OF WATER, AIR, SOIL, AND MILK 



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



Bacteriological examinations of water are, in a measure, very 

 disappointing, because it is difficulty 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 faeces 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 faeces, and 

 perhaps typhoid faeces. The detection of the colon bacillus is 

 therefore of prime importance in the examination of drink- 

 ing water. Its detection is simple. Water must be collected 

 in sterile bottles, using every precaution against accidental 

 contamination. Fermentation tubes are employed, containing 

 bouillon with i percent of lactose. Into a series of these tubes, 



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