EIS 
sun. We have never yet discovered a well sunned sample 
of surface water from which this organism may not be iso- 
lated, and if the pollution is old the organism is extraordinarily 
common. The following appear to be the various fermen- 
tative reactions of this bacillus :— 
The organism does not ferment lactose, but after it has 
been subcultured for some time in the laboratory a very faint 
trace of acid, though no gas, is sometimes seen. This is 
rather interesting, and at one time we thought it. was remotely 
possible that this bacillus. was really a true lactose fermenter 
which had lost its power of fermenting this sugar owing to 
exposure to the sun. Further experiments and consideration, 
however, have negatived this view. Acid and gas are produced 
in large amount in both glucose and saccharose. Neither acid 
nor gas is produced in mannite, dulcit, adonit and inulin. 
The organism does not liquefy gelatine within Io days, nor 
does it give theindol reaction. The Vosges and Proskauer’s 
reaction is given very strongly. In litmus milk there is’ 
a very slight acidity at the top of the tube in some cases, but 
no clot is produced. The bacillus is very actively motile 
and is gram positive. The bacillus has all the usual appear- 
ances of coli communis under the microscope, but gives a 
rather opaque white colony on neutral red lactose agar. 
These are the characteristics of bacillus P. The other 
important point is as already stated, its ubiquity. 
Let us briefly recapitulate what are the various stages 
that occur in the self-purification of natural water, such as 
a lake after it has been heavily polluted bysurface washings. 
We start with a gross recent pollution the indications of which 
as we have already seen are :— 
(1) The truly fecal nature of the mixture of organisms 
isolated from a sample. 
(2) The presence of susceptible organisms, particularly 
coli communis, oxytocus perniciosus, etc. 
(3) Identically the same result .is obtained in a 
glucose and lactose broth; acid and gas line 
the same in both. 
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