66 



ELEMENTS OF WATER BACTERIOLOGY 



numbers up to 65,000 per gram in roadside mud. In 

 an examination of water from the Charles River above 

 Boston, 37° counts ranging from 9800 to 16,900 have 

 been found. The average result of 56 examinations of 

 Boston sewage from July to December, 1903, showed 

 5,430,000 bacteria per c.c, at 20° and 3,760,000 per 

 c.c. at 37°, of which 1,670,000 were acid formers. The 

 average of 25 samples examined in July and August, 

 1904, showed 1,690,000 bacteria per c.c. at 20° and 

 1,400,000 at 37°; 429,000 per c.c. twere acid formers 

 (Winslow, 1905). 



In unpolluted waters not only the absolute number of 

 organisms developing at the body temperature is less, but 

 its ratio to the gelatin count is very different. Rideal 

 (Rideal, 1902) states that the proportion between the 

 two counts in the case of a London water in a year's 

 examination was on the average one to twelve. Mathews 

 (Mathews, 1893) in 1893 gave the following figures, 

 the contrast between the ponds and streams, which 

 were presumably exposed to pollution, on the one 

 hand, and the wells, springs, and taps, on the other, 

 being marked. 



Source of Water 



Average Number of Colonies per c.c. 



