84 BACTERIA 



the water on into the lower and more absorptive parts of the 

 alimentary canal. Such a condition of affairs clearly in- 

 creases the danger of water-borne germs. 



THE BACTERIOLOGY OF SEWAGE AND SEWAGE-POLLUTED 



WATERS 



It will not be needful to insist upon the obvious fact that 

 bacteria abound in sewage. Such a large quantity of organic 

 matter, in which decomposition is constantly taking place, 

 will afford an almost ideal nidus for micro-organic life. 

 There is indeed but one reason why such a medium is not 

 absolutely ideal from the microbe's point of view, and that 

 reason is, that in sewage the vast number of bacteria present 

 make the struggle for existence exceptionally keen. Not 

 only are the numbers incredibly large, but we also find a 

 very extensive representation of species, including both 

 saprophytes and parasites, non-pathogenic and pathogenic. 

 Not infrequently it is from pollution by sewage that drink- 

 ing water is contaminated with disease. A patient, we will 

 say, suffers from typhoid fever. The specific organism has 

 its habitat largely, though not exclusively, in the alimentary 

 canal. It passes out in the excreta, and though sometimes 

 partially disinfected, may escape without hindrance into the 

 drains, and thus to the sewer or cesspool. How often, by 

 means of direct connection or by percolation, sewage, from 

 sewers or cesspools, gains access to drinking water, the 

 history of typhoid outbreaks in this country only too fully 

 records. 



It is impossible to lay down any exact standard of the 

 chemical and bacteriological quality of sewage. The qual- 

 ity will differ according to the size of the community, the 

 inclusion or otherwise of trade-waste effluents, the addition 

 of rain-water, and other like physical conditions. Moreover, 

 sewage itself when, so to speak, fully formed is liable to 

 undergo rapid changes owing to fermentation and the com- 



