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(2) It is probably not realised by those unacquainted 
with tropical conditions how extremely commonly samples 
of water containing resistant organisms alone are met with. 
It appears to us doubtful whether such samples are ever 
found in Europe. Consequently whenever such samples are 
found they may be looked upon as safe, as far as their chances 
of spreading disease is concerned, in spite of the fact that 
both lactose fermenting and glucose fermenting organisms 
are extremely common in the samples. Other confirmatory 
evidence as to the correctness of this dictum will be found 
in that the acid and gas line in glucose and lactose broth is 
widely separate; that the lactose fermenting organisms do 
not show a large number of varieties, but are usually a pure 
culture of either bacillus vesiculosus or bacillus cloace. 
(3) Those containing a mixture of two or more classes ; 
the chief difficulty that will be met with by an analyst using 
this method will be to arrive at an opinion from samples 
showing a mixture of classes 2 and 3. It is when dealing 
with samples of this kind that it is absolutely necessary to 
know particulars concerning where the samples come from, 
the amount of rainfall, etc. It must also be borne in mind 
that in the hot weather the number of varieties of organisms 
in feces generally seems to fall off. Consequently one must 
not expect too many varieties even with a recent contam- 
ination. Another difficulty is the fact that such organisms as 
bacillus vesiculosus are extremely common in perfectly fresh 
feces. Consequently too great stress must not be placed on 
their presence in samples of water containing this mixture 
of classes 2 and 3. In attempting to arrive at a conclusion 
one must be guided by (z) the actual number of fecal 
organisms present in the sample; (7) the results obtained 
from the acid and gas line in the glucose and lactose broth ; 
(221) the presence or absence of a large number of bacillus 
lactis erogenes. A water containing a large number of this 
organism shows that it has reached the stage of “lactis 
ezrogenes prevalence,’’ and has departed thus far from the 
original fecal arrangement. This fact taken with the acid 
and gas line in glucose and lactose will be found to give the 
best indication as to the date of pollution, but it is admit 
