THE EXAMINATION OF WATER 649 



(9) The B. cloacae and B. grunthal will persist in water exposed to 

 the action of sun and storage for many months, and may 

 therefore be looked upon as resistant to these forces. 



(10) The rareness (^)f su(~h organisms as CoH communis in the 



samples analysed demonstrates the fact that organisms very 

 susceptible to the action to sunlight do exist, Coli communis 

 being the commonest of these. 



(11) Storage in the tropics is capable of rendering a highly con- 



taminated water exlremelv pure, and of killing a large number 

 of the faecal organisms present after gross pollution. 



In estahlishlui^ bacterial standards, for drinking-water in India, a 

 preliminary grouping is given to us thus : — 



Class (i). — See (3), (a) above. 



Those Avaters containing Coli communis and the members of the 

 susceptible group. 



The contamination is recent and dangerous. 



These are not commonly found. 



Class (2). — See (3), (c) above. 



Those Avaters containing such resistant organisms as B. grunthal, 

 or B. cloaca? or both. 



These represent a pollution months old from a water supply becom- 

 ing exhausted. 



Class (3). 



Those waters containing both the above organisms. 



This condition is to be expected in rainy weather and flooded rivers. 



In general be guided by : — 



The number of faecal organisms present. 



The number of different species present in the ten colonies isolated. 



To which group the organisms tend to belong most. 



In fresh samples of fa?cal contamination the Lactis aerogenes is not 

 often present, hence if it is found it may be considered as evidence that 

 a considerable amount of purification of the water has taken place. 



Clemesha proposes to classify river waters thus: — 

 (i) Good river water. 



This should not contain more than 100 colonies on a (jar at 



o 



Ftecal organisms should not exceed one in 10 c.c. 

 No organisms in Class (i) should be present in 50 c.c. 

 Ffecal organisms present should belong to either Class (3) or 

 the more resistant group of Class (2). 

 (2) Fair or usable river water. 



This should not contain more than 300 colonies on agar at 



o 



7° C. 



