CHAPTER ¥, 
THE PREVALENCE AND SIGNIFICANCE OF STREPTOCOCCI 
IN WATER. 
Tus subject follows closely on what has gone before, 
and, as no very great amount of space will be required in dis- 
posing of it, it seems advisable to complete the study of strep- 
tococci and their significance in water supplies. 
We have already shown that streptococci are extraordin- 
arily common in feces both of man and animals. Conse- 
quently it is obviously necessary to devote a certain amount 
of attention to an enquiry into what becomes of the millions 
of streptococci which undoubtedly pass into surface water 
along with feces. In order to elucidate this problem two 
separate series of researches have been carried out. First 
of all our routine samples of water which come into our labor- 
atory from various town supplies, rivers, lakes and wells, 
etc., have been carefully examined for the presence of these 
cocci. Secondly, experimental mixtures of feces and water 
have been examined under varying conditions. 
Before proceeding, it may perhaps be well to mention 
that the method of searching for streptococci in water does 
not differ materially from that already described in the fore- 
going chapter. For raw waters, we take 20 c.c. of the sample, 
centrifugalise it for a period of a quarter of an hour in a 
centrifuge, the sediment is carefully pipetted off, put into 
lactose broth, from this on to large Conradi Drigalski plates. 
The small colonies are picked off, examined under the 
microscope to see if:there are true streptococci, they are 
then tested by putting them through the following reagents, 
—milk, mannite, lactose, saccharose, salicin and raffinose 
broth. The method is identical with that used by Houston 
except that for his raw water I c.c. appears to be usually suffi- 
cient. 
From a very careful study of many samples from rivers, 
lakes, and wells we find that the number of occasions on 
