122 BACTERIOLOGY 



CHAPTEE YI 



THE BACTERIOLOGICAL ANALYSIS OF WATER 



Micro-organisms of water. Water, both in its liquid 

 and solid state, almost always contains micro-organisms, 

 although in variable quantity, and these have been named 

 water bacteria by Percy Frankland. They are for the most 

 part bacilli in general such as do not liquefy gelatine and 

 they do not grow at the higher degrees of temperature. 

 Some of them have the property of setting up ammoniacal 

 fermentation. But pathogenic varieties are also found, in 

 the foremost rank of wKich stand the cholera bacillus de- 

 scribed by Koch, which was discovered in drinking water in 

 the neighbourhood of Calcutta, and the bacillus of typhoid 

 fever ; but besides these, others also occur as a contamination 

 of water. Some micro-organisms cannot grow in water 

 alone, as it does not afford sufficient pabulum for their 

 development, but large numbers also perish from being 

 overwhelmed by the growth of the water bacteria. 



Very many of the micro-organisms met with in water 

 generate pigment, often in such quantity that considerable 

 volumes appear coloured or fluorescent owing to it, and a few 

 exhibit a brilliant phosphorescence. 



Filtration and filters. Microbes are removed from water 

 bj filtration, for which purpose use is made of sand filters 

 constructed with sand and gravel, charcoal filters of plastic 

 carbon, filters of asbestos, of unglazed porcelain, of earthen- 

 ware made from burnt diatomaceoiis clay, &c. Forster's filter 



