BACTERIA DEVELOPING AT DIFFERENT TEMPERATURES 245 



The normal ratio between the 20 and 30 bacteria for the Merri- 

 mack River samples appears to be about 5, 40 per cent of the samples 

 having ratios between i and 5, 9 per cent being below i, and the 

 remaining 51 per cent being well distributed above 5. As the waters 

 become purer, the ratios become more varied. The normal limit for 

 Applied 216 is still between i and 10, but is apparently somewhat 

 higher than in the case of the river water. The normal limit for 

 the effluent from Filter No. 216, like the river water, is between 

 i and 5, but the majority of the other ratios fall below rather than 

 above those limits. The purer effluents from the water filters oper- 

 ating at low rates are characterized by the large percentage of samples 

 having ratios of o, and by the distribution of the remaining samples 

 among the higher ratios, which fact is still further emphasized when 

 we come to the pond waters. 



The normal ratio between the 20 and 40 bacteria again falls be- 

 tween i and 5 for samples from the Merrimack River and from Ap- 

 plied 216. In the same group must be included the effluent from 

 mechanical Filter No. 216. The ratios for the other water filters are 

 more widely distributed, 19 per cent of the samples not showing any 

 growth at 40, and 37 per cent having ratios above 15. The group 



TABLE 12. 



DISTRIBUTION OF THE RATIOS BETWEEN 20 BACTERIA AND BACTERIA AT 30 AND 40 AMONG 

 DIFFERENT SAMPLES FOR VARIOUS CLASSES OF WATERS. 



FOR RATIOS BETWEEN 2O AND 30 BACTERIA. 



FOR RATIOS BETWEEN 2O AND 40 BACTERIA. 



