300 WATER HYGIENE 
that B. coli is not present in a water except it has received sewage pol- 
lution. These, however, may be extreme opinions and may not repre- 
sent the opinions of the sanitarians in cach country. Race (1914, 1916) 
argues that B. cola is a reliable indicator of pollution and states that those 
cities which have many B. colz in their water usually have a high typhoid 
fever death rate. He warns that B. colz should be regarded as merely an 
inferential indicator. The fact that the presence of B. colz in a sample 
of water may not be sufficient evidence of serious pollution, it is, how- 
ever, a danger signal which must not be overlooked. Houston (1915) 
representing the English practice regards B. coli as the best index for the 
control of purification processes. Winslow (1916), in tracing the history 
of this organism as an indicator has advised the accumulation of as much 
data as possible to more definitely determine whether B. colz is purely a 
fecal form and B. aerogenes a saprophytic form. 
The testing of water for this organism has taken some recent advances. 
Thanks to the research of Rogers and his co-workers in the laboratories 
of the Bureau of Animal Industry, we have now fairly reliable methods 
for differentiating between fecal and non-fecal B. cold. The methods of 
analysis which are given in the following pages have been taken with 
permission from the 1917 report of the committee on water and sewage 
analysis of the American Public Health Association. 
American Public Health Association Method for Determining the 
Presence of Members of the B. coli Group. It is recommended that 
the B. coli group be considered as including all non-spore-forming bacilli 
which ferment lactose with gas formation and grow aerobically on 
standard solid media. 
The formation of 10 per cent or more of gas in a standard lactose 
broth fermentation tube within twenty-four hours at 37° C. is presump- 
twe evidence of the presence of members of the B. coli group, since the 
majority of the bacteria which give such a reaction belong to this 
group. 
The appearance of aerobic lactose-splitting colonies on lactose-litmus- 
agar or Endo’s medium plates made from a lactose-broth fermentation 
tube in which the gas has formed confirms to a considerable extent the 
presumption that gas-formation in the fermentation tube was due to 
the presence of members of the B. coli group. 
To complete the demonstration of the presence of B. coli, as above 
defined, it is necessary to show that one or more of these aérobic plate 
colonies consists of non-spore-forming bacilli which, when inoculated 
into a lactose-broth fermentation tube, forms gas. 
It is recommended that the standard tests for the B. coli group be 
