6 
shall show further on that all members of this group are not 
equally indicative of undesirable pollution. Thus, supposing 
A and B two separate organisms in this group, A may be 
found in nature to multiply in water, or to remain at the 
bottom of lakes for long periods. On the other hand, B may 
be clearly shown to disappear in a few days. Obviously, 
therefore, the significance of these two organisms would be 
different when looked at from the point of view of their pres- 
ence in any sample of water. The point it is necessary to 
emphasize is, that a careful study of the natural phenomena 
of self-purification of water will tell us something of value 
concerning the life-history of individual species of fecal 
organisms ; classifying organisms into artificial classes according 
to their action on certain sugars does not tell us anything. 
It appears to us that there is a tendency among water ana- 
lysts generally to stick too closely to certain standards, useful 
though they may be, rather than to go to Nature herself for 
our information. It has already been stated that the arbi- 
trary rules which are admittedly fairly satisfactory in England, 
would be worse than useless in India. Of course, classifi- 
cation of organisms according to their fermentative reaction 
is necessary in order to describe them. Thus, we shall use 
the term ““ lactose fermenters;’’ “* glucose fermenters 7 ame 
alsoa group of organisms which are ‘‘ glucose +, lactose—,’” 
but we wish it to be understood clearly from the very outset, 
that we never for a moment suppose that all organisms which 
ferment the same sugar, possess similar characteristics in 
other respects, or behave similarly when passed into water, 
and subjected to natural forces. _ In fact, we shall show clearly 
that this is not the case. 
If any classification of organisms is necessary, a much 
more satisfactory method, from the point of view of water 
analysts, is to divide them according to their ability to live in 
water exposed to sunlight. Class I containing the susceptible 
organisms which rapidly die out on exposure to sun’s rays : 
Class III the resistant bacilli, or those which will remain weeks, 
or months, in water: Class II the intermediate species, about 
which less is known. The fact that one variety of fecal 
organisms will live 6 months at the bottom of a lake is worth 
