BACTERIA DEVELOPING AT DIFFERENT TEMPERATURES 243 



A study of the bacteria-5. coli ratios reveals that those ratios also 

 have been constantly higher for the Intake samples than for the canal 

 samples, and that there has been a greater uniformity in the bacte- 

 rial content of the Merrimack River water after it has passed through 

 the canal and the short distribution pipes to the experimental niters 

 at the Experiment Station, taking the results year by year, and 

 month by month, than was the case with the same water as it was 

 applied to the Lawrence City Filter. 



The average ratio on all samples collected from the Intake during 

 the entire seven years was 1.12, the lowest yearly average being 

 0.81, in 1899, and the highest 1.63, in 1900. The lowest monthly 

 average occurred in August, 1899, and again in December, 1901, 

 when the ratio was 0.16, and the highest monthly average, 6.30, 

 occurred in March, 1900. The least variation in the monthly ratios 

 for any one year occurred in 1904, the difference between the high- 

 est and lowest values in that year being 1.27. The greatest varia- 



TABLE ii 



AVERAGE MONTHLY BACTERIA B. coli RATIOS ON SAMPLES FROM THE MERRIMACK RIVER FROM 

 THE NORTH CANAL, i8o8-iQo<; INCLUSIVE. 



tion in the monthly ratios in any year occurred in 1900, when the 

 difference between the highest and lowest ratios was 6.08. 



The average ratio on all samples from the canal during the entire 

 period of eight years was o . 98, the lowest yearly average being 

 0.80, in 1899, and the highest 1.41, in 1905. The lowest monthly 

 ratio occurred in October, 1901, when the ratio was 0.08, and the 

 highest occurred in August, 1905, when the ratio was 2.66. The 

 least variation in the monthly ratios during any one year occurred in 



