316 WATER HYGIENE 
than 10. What bacteriological proof would you consider conclusive that 
a water is free from such pollution or so free that it is safe for drinking 
purposes? Houston regards the absence of B. coli from 100 c.c. of the 
deep well water as reasonably sufficient evidence of safety and the greater 
the number of these negative results, the more satisfactory is the water. 
A water which never contains B. cols in 100 c.c. quantities is to be 
regarded as a safe drinking water. A water which contains B. coli in 
less than half of the samples examined occupies an intermediate posi- 
tion but is probably reasonably safe. One which contains B. coli in more 
than half should be regarded with some preliminary disfavor. 
Winslow replied to these questions and stated that the presence of 
colon bacilli in all of ten duplicate 10 ¢.c. samples, is reasonable proof 
of the presence of sewage or manurial matter while the absence of colon 
bacilli from such samples would be reasonable proof of the absence of 
such sewage. Winslow would carry out a confirmative test to show 
that the fermentations were due to true B. colv. 
McLaughlin (1914) regards a safe water as one which contains no 
pathogenic bacteria. According to his opinion a water containing no 
more than 2 B. colt per 100 c.c. is satisfactory. A filter plant that can- 
not furnish such an effluent is either inefficiently operated or is handling 
a raw water which imposes an unreasonable load on the filters. 
In light of the recent contributions of Rogers, Clark and Lubs on 
the differentiation of the members of the colon group, in which they 
have shown that B. colz of fecal origin is methyl red plus (+) careful 
extensive work must be done in the future to work out the relation of 
the methyl red test to the analysis and control of water supplies. Clark 
(1918) has advised this. Orchard (1918), in view of the lack of uni- 
formity concerning standards has recommended that the societies con- 
cerned with water analysis appoint committees to study this problem. 
This would probably be the quickest and most reliable method of 
handling the question. 
Wording of Reports on the Results of Bacteriological Examination of 
Water. This is often a difficult procedure for the analyst especially if 
the certificate accompanying the sample is not filled in. An investiga- 
tion of this question reveals the lack of uniformity in reports from dif- 
ferent laboratories on the same sample of water. This was realized 
among the English analysts to such an extent that a committee of the 
Royal Institute of Public Health was appointed to go over the subject. 
They reported as follows: When the source and surroundings are un- 
known, it is undesirable to report as follows: 
“This water is grossly polluted and is dangerous for drinking ” or 
