286 WATER IYGIENE 
CLASSIFICATION OF WATER BACTERIA 
The water bacteriologists have been primarily interested in the pres- 
ence of certain bacteria which are of sanitary significance. They have 
done very little with the other bacteria that may be in water with which 
they are dealing but have confined their attention to some ten organisms 
which indicate pollution. Only after the other branches of the science 
had become well advanced did water bacteriologists give any attention 
to classification. This may have been due to the fact that the flora 
of a water is heterogeneous and that a few bacteria are probably secured 
from each material with which the water comes in contact. The en- 
vironment of a water determines its bacterial flora. One coming from 
an unpolluted water shed will have quite a different flora than a water 
flowing from a river which is made to carry the wastes of industrial and 
domestic life. Each of these examples would have a constant flora but 
one characteristic for the case mentioned. With the exception of pos- 
sibly ten bacteria or groups whose presence is supposed to indicate 
pollution, very little is known about the large number of other bacteria 
which may be present. More accurate deductions might be made with 
regard to the sanitary character of a sample of water could more be 
known concerning its bacterial flora. This question has been discussed 
in Standard Methods for the Examination of Water and Sewage for 
1912, page 106. ‘‘ In certain cases the determination of species may play 
directly a useful part in water analysis. It sometimes happens that the 
bacteria present in a filtered water are different in character from those 
found in the raw water and unless the facts are known, erroneous infer- 
ences may be drawn as to the efficiency cf the filters. The determination 
of particular species is sometimes of importance in proving the identity 
of a water from a particular source. At times also, the presence of cer- 
tain species in water may be indicative of pollution.” . 
Bacterial control of filter operations is very important when the 
health of the public depends upon this factor. A knowledge of the 
general flora of the raw water might, at certain times, be a valuable 
factor in determining the efficiency of the filters.” This would tell 
whether the bacteria in the effluent were passing through the filters 
from the raw water or whether they were growing in the under drains. 
Certain bacterial standards have been formulated that place the limit 
of 100 per cubic centimeter for bacteria in the filtered water. The 
character of the bacteria in those effluents which contain more than 100 
per cubic centimeter would be very important. 
