BACTERIOLOGY 

 PART II 



CHAPTER I 

 EXAMINATION OF WATER 



Water which may be considered potable, without suspicion, contains few 

 or no bacteria and no pathogenic bacteria (no colon bacilli). Most water con- 

 tains some bacteria. That which shows 100 colonies per cubic centimeter or 

 less, none of which are pathogenic, should be considered safe. When 500 

 colonies per cubic centimeter or more are present, even though none of them are 

 pathogenic, it must be considered with suspicion, because where so much bac- 

 terial life can be found in water, as a rule, conditions are favorable for the 

 entrance of disease-producing germs at any time. 



Colon bacilli in water are not always of human origin ; in populated districts 

 they usually are and hence we are compelled to consider the presence of colon 

 bacilli in water evidence of dangerous contamination. 



Colon bacilli in water, of themselves, probably do not constitute a grave 

 danger, but experience has shown that, as a rule, colon bacilli in water indicates 

 pollution with human sewage, and such pollution eventually results in an 

 epidemic of typhoid fever, cholera or other water-borne diseases. 



It is always difficult, frequently impossible, to detect and isolate typhoid 

 bacilli and other pathogenic bacteria from water, even when such organisms are 

 known to be in it. The colon bacillus can be detected and isolated with com- 

 parative ease; hence, water is examined for colon bacilli and judged as good or 

 bad, according to the presence or absence of the colon bacillus. 



Efficient chemical treatment or nitration not only removes or destroys all 

 pathogenic bacteria and colon bacilli, it removes or destroys more than 95 per 

 cent, of the total bacterial content. Hence, in estimating the efficiency of 

 chemical treatment or filtration, samples are obtained before and after treat- 

 ment and examined to determine the number of bacteria per cubic centimeter, 

 also for colon bacilli. 



To get a fair sample for examination, when water is obtained from a tap or 

 faucet, the water should be allowed to flow for at least 5 minutes before col- 

 lecting a specimen. 



If it is to be obtained from a spring, lake or stream the person collecting 

 should wash his hands and then submerge the container before opening it. The 

 container should be kept submerged until it is full and has been closed or 

 stoppered. 



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