18 



ROYAL SOCIETY OF CANADA 



three months. This number (li) must be subtracted from our monthly 

 colon figures after correction with the dilution factor. For example^ 

 for the month of April the number 14 must be divided by 4, so that 

 only 31/^ is subtracted from the monthly estimation of B. coli (151) — 

 3^ = 12, which indicates the colon contamination per c.c. from other 

 sources. 



The monthly average number of bacteria growing on beef peptone 

 «gar at 37 °C. is included in the following table. 



Table Showing Colon Contamination From Ottawa Sewerage and Other 



Sources. 



Month 



Bacteria per c.c. 

 on agar. 



Total B. coli 

 per c.c. 



B. coli of 



sewage origin 



per c.c. 



B. coli from 



other sources 



per c.c. 



April 



May 



June 



July 



August 



September . . 



October 



November. . ■ ■ 



December 



January. 



February 



March 



April 



1,600 



200 



1,700 



300 



400 



4,175 



1,400 



9,600 



150 



200 



75 



30 



200 



15H 

 12 

 9 



37K 

 88 

 24 

 *50 



22^ 

 16 

 5 

 13 



14 



4 

 14 



= 3^ 



6»^ 

 14 



5 

 14 



2^ 

 14 



14 



1 

 14 



1 

 14 



14 



IH 

 14 



14 



1^ 

 14 



2 

 14 



= 3 



= 9 



= 14 



= 14 



= 9 



= 9 



= 9 



= 9 



= 7 



= 4M 



12 



10 

 G 

 



28M 

 74 



10 



41 







13M 

 7 

 

 8H 



*One exceptional analysis of 2,600 B. coli per c.c. is omitted. 



