SIGNIFICANCE OF COLON GROUP IN WATER 153 



animal sort." Pakes (Pakes, 1900) stated on the 

 strength of an examination of " about 300 different 

 samples of water," no particulars being published, that 

 water from a deep well should not contain B. coli at 

 all, but that water from other sources need not be con- 

 demned unless the organism was found in 20 c.c. or less. 

 When colon bacilli were found only in greater quantities 

 than 100 c.c. the water might be considered as probably 

 safe. Horrocks (Horrocks, 1910), after a general 

 review of English practice, concluded that " when a 

 water-supply has been recently polluted with sewage, 

 even in a dilution of one in one hundred thousand, it 

 is quite easy to isolate the B. coli from i c.c. of the 

 water." " I would say that a water which contained 

 B. coli so sparingly that 200 c.c. required to be tested 

 in order to find it had probably been polluted with 

 sewage, but the contamination was not of recent date." 

 Chick (Chick, 1900) found 6100 colon bacilli per c.c. 

 in the Manchester ship canal, 55-190 in the polluted 

 River Severn, and numbers up to 65,000 per gram 

 in roadside mud. On the other hand, of 38 unpolluted 

 streams and rivulets, 31 gave no Bacillus coli and the 

 other 7 gave i per c.c. or less. The Liverpool tap water, 

 snow, rain, and hail showed no colon bacilli. 



One of the first elaborate applications of the colon 

 test was made by Jordan in the examination of the fate 

 of the Chicago sewage in the Desplaines and Illinois 

 Rivers. In these studies of self-purification (Jordan, 

 1901) the analyses were made quantitative by the 

 examination of numerous measured samples, fractions 

 of the cubic centimeter; and the method employed 



