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(ii) that the relation between the two classes of organ- 
isms varies at different times of the year in natural 
samples of surface water. That the divergence 
is greater in summer than winter ; 
(277) that in lake waters the divergence is more marked 
than in river waters ; 
(iv) that experiment and a careful study of rivers and 
lakes shows that the high acid and gas line in 
glucose is due to the presence of bacillus P which 
multiplies in water ; 
(v) speaking broadly the more recent the pollution is, 
the nearer together is the acid and gas line in 
glucose and lactose broth, the older it is, the 
greater the divergence ; 
(vt) that the best way of estimating the numbers of the 
glucose + lactose—and glucose + lactose + fecal 
organisms is by using the same quantity of the 
water in the two broth media. 
