BIOLOGICAL WATER ANALYSIS 1 17 



the colon bacillus test should be supplemented by the plate count 

 and the examination of the centrifugalized sediment. 



Although the bacteriological examination of water supplies is 

 the work of the sanitarians, the food bacteriologists are frequently 

 called upon to pass judgment on the potability of water supplies. 

 There is no definite numerical standard for drinking waters. In 

 the United States the presence of the colon bacillus is almost wholly 

 the basis for condemnation, it being assumed that if bacteria are 

 present in great numbers the colon bacillus is also generally present. 

 This is, however, very frequently not the case. Distilled water may 

 contain numerous bacteria without any colon organisms. Stag- 

 nant waters may contain bacteria in great numbers without colon 

 bacilli. It is not practicable to adopt an arbitrary numerical 

 limit as has been suggested by various investigators. Miquel 

 (1891) suggested the following standards: 



10 bacteria per cc. or less Excessively pure 



10-100 bacteria per cc Very pure 



100-1000 bacteria per cc Pure 



1000-10,000 bacteria per cc Mediocre 



10,000-100,000 bacteria per cc Impure 



100,000 and more bacteria per cc Very impure 



German sanitarians generally recognize a limit of 50 to 300 for 

 drinking water. Dr. Sternberg of the Public Health Service (1892) 

 suggested that less than 100 bacteria per cc. indicated a deep source 

 of the water supply and uncontaminated by surface drainage and 

 that a water supply with 500 bacteria per cc. was open to sus- 

 picion and that 1000 and over is presumptive indication of sewage 

 contamination or of surface drainage. It is quite evident that 

 there is very little excuse for the use of city and other communal 

 drinking water supplies with a count higher than 5-10,000 per cc., 

 and it is suggested that this be made the numerical limit for drink- 

 ing water in the absence of or irrespective of the presence of the 

 colonjDacillus. 



The general routine for making the tests for the presence of the 



