246 



STEPHEN DEM. GAGE 



of sea waters, containing, as it does, samples probably not exposed 

 to pollution, and samples which are grossly polluted, shows a more 

 uniform distribution of ratios than any of the other classes of waters, 

 although the normal ratio for samples containing bacteria which are 

 able to grow at 40 appears to lie between 5 and 10. The distinc- 

 tion between the pond waters and the well waters is quite marked 

 Forty-nine per cent of the pond samples and 42 per cent of the 

 well samples did not contain any bacteria growing at 40 C. Of 

 the samples which did contain bacteria of this type, nearly all of the 

 pond samples have high ratios, while the ratios for the well samples 

 are usually very low. The percentage distribution of the different 

 ratios between the 20 bacteria and the bacteria determined at 30 

 and 40 for different classes of waters is shown in Table 12. 



The normal ratios between the 20 bacteria and the jo acid-pro- 

 ducing organisms follow much the same rule as the 2O-3O bacteria 

 ratios, the distinction between the different classes of water, however, 

 being much more sharply marked. The normal ratio for Merri- 

 mack River water lies between i and 5, and with a large majority 

 of the ratios above 5, falling below 10. With the Applied 216, while 

 the normal ratio lies between the same limits as for the river water, 

 the other ratios are about evenly distributed above and below those 

 limits. Again, with the effluent from Filter No. 216 the normal 

 ratio is between 5 and 10, but the number of samples having ratios 



TABLE 13. 



DISTRIBUTION OF RATIOS BETWEEN 20 BACTERIA AND 30 ACID-PRODUCING BACTERIA AMONG 

 DIFFERENT SAMPLES FOR VARIOUS CLASSES OF WATERS. 



above 5 is small, and a considerable percentage of the samples did 

 not show acid-producing bacteria. As we pass to the effluents from the 

 slow water niters, and thence to the pond waters, the percentage of 

 samples free from acid-producing bacteria increases, while the normal 



