294. WATER HYGIENE 
count for the shortest incubation period is secured at 27° C. Gelatin 
was found to yield the highest count. Hill (1908) and Breed and Dot- 
terer (1916) have given some interesting data to show that a good agar 
plate should not contain over 200 bacteria when counts are to be made. 
These investigators show that a plate which has less than about 20 and 
over about 200 bacterial colonies will give a count which is not accurate. 
INDICATORS OF POLLUTION 
As soon as sanitary science had demonstrated that diseases were 
spread by polluted water and foods, it became necessary to find some 
method of detecting the presence of fecal matter. With this effort 
originated the Bacillus colon test which has passed through many stages 
to reach its present status. Other ‘“ indicator” organisms have been 
used in bacteriology such as the streptococci and Bacillus enteridins 
Gaertner. Indicators of pollution in bacteriology have certain definite 
characteristics. 
1. They should be present in water and on foods which have received 
sewage pollution. 
2. They should be absent from foods which have not, been in contact 
with sewage. ; 
3. They should be easily detected in the shortest time consistent 
with accurate results. 
4, They should possess constant characteristics and not be subject 
to either morphological or physiological changes. 
From the above, it is apparent that an ideal indicator does not exist. 
Admitting this, the analyst has to resort to the next best thing and take 
an indicator which best fulfills the necessary requirements. The relative 
amount of the indicator has come to be the important factor and not the 
mere presence of the indicator. 
The Streptococci. The examination of water for streptococci is 
not used in America for the routine examination. It would probably 
be of much value were it used in this country. Houston (1898-9) 
originally emphasized its value. Possibly one reason why the strep- 
tococci are not used in routine analysis is the lack of methods for dif- 
ferentiating fecal and non-fecal streptococci. Winslow (1902) and 
Fuller and Armstrong (1913) pointed out that the amounts of acid 
formed in carbohydrate media might be used as bases for differentiation. 
Armstrong and Fuller found that human fecal streptococci were char- 
acterized by high acidities in glucose, lactose, and mannite broths and a 
low acidity in raffinose broth. On the other hand equine and bovine 
