Bacteria Developing at Different Temperatures 243 



A study of the bactcria-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 filters 

 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, ^"d 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 n 

 Average Monthly Bacteria — B. coli Ratios on Sauples from the Merrimack River from 



THE North Canal, i8q8-ioo.s Inclusive. 



January 



February 



March 



April 



May 



June 



July 



August 



September . . . 



October 



November. . . . 



December 



Average. . 

 Maximum 

 Minimum 



1898 



.80 

 •59 

 • 4.S 

 .20 

 70 

 ■56 



. 12 

 . 12 



■75 

 ■55 

 07 

 65 

 07 

 . 12 

 ■45 



1899 



0.83 

 0.45 

 o. 20 

 0.65 

 0.82 

 0.97 



2. 50 

 0.78 

 0.41 

 O. I T 

 0.62 

 0.93 



O .80 



2 . 50 

 O. II 



1900 



0.47 



O .60 



0.61 



o. 70 



0.98 



1.96 

 2-59 



1.08 

 0.71 



46 



24 



53 

 .08 

 59 

 46 



1901 



2.56 

 2 .42 

 1. 41 

 1 . 10 

 0.83 

 0.44 



47 

 16 



32 

 08 



27 

 31 

 95 

 56 

 08 



1902 



0.52 

 0.61 

 o. 14 

 1.86 

 1-37 

 0.60 

 043 

 I 94 

 0.97 

 0.91 

 098 

 0.66 

 0.92 

 1.94 

 o. 14 



1903 



0.39 



0.44 



0.61 



06 



95 



65 

 90 

 87 

 57 

 70 

 40 

 49 

 75 

 40 

 39 



1904 



95 

 22 



37 

 50 

 81 



93 



il 



88 



1 .00 

 0.86 

 038 



1 .01 

 232 

 0.37 



lOOS 



21 



00 

 II 



43 

 54 

 94 

 26 

 66 



OQ 



63 

 45 

 54 

 41 

 66 



63 



Average 



0,97 

 0.92 

 0.62 

 1 .06 

 I 01 

 0.88 



1 57 

 '43 

 0.96 

 o. 56 



O 90 



O 81 



o 98 



2 66 

 0.08 



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 0.98, 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 



