CHAPTER XIII. 



BACTEEIOLOGICAIi EXAMINATION OF WATEE. 



Even not counting the exceptional cases, wlien tlie 

 presence of bacteria in water is suspected during an 

 epidemic, the bacteriological examination of water is 

 of great practical importance. Chemical analysis alone 

 is not sufBcient ; for, as regards one of the most 

 important points, i.e. the determination of the amount 

 of organic matter present in the water, it is not to be 

 relied upon. If the quantity held in solution be 

 small, neither its composition nor its exact amount can 

 be gauged by the ordinary methods with any degree 

 of accuracy. 



Bacteria form a delicate test for this organic matter, 

 for just those substances which originate in human 

 habitations, the products of decomposition of organic 

 substances, which get into the water from dung-pits, 

 drains, dirty canal water, water from manufactories, 

 etc., afford them excellent nourishment, whilst other 

 organic substances, such as those from peat heaps or 

 bogs, are useless to them. It is true that very prob- 

 ably the peaty or boggy water contains far more 



