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the average was 1,275,000, and in the 3 samples corresponding to the 6-foot secondary coke-bed
effluents 1,000,000. Calculated from these figures the percentage reduction of liquefying bacteria
was 18 as regards the 4-foot coke-bed effluents, 34 in respect of the 6-foot primary coke-bed
effluents, and 16 as regards the 6-foot secondary coke-bed effluents.
Usually a rise or fall above or below the mean in the number of liquefying bacteria in the
crude sewage was associated with a similar increase or decrease in the number in the corresponding
effluents. Thus as regards the crude sewage and 4-foot coke-bed effluents, in 10 out of the 15
experiments there was a correspondence, and in the case of the 6-foot primary coke-bed effluents,
4 out of the 8 samples corresponding to the crude sewage showed a similar relationship. Only
3 samples of the effluent from the 6-foot secondary coke-bed were examined; these in each case
were related to the raw sewage in the above sense.
So far as may be judged from a rise or fall above or below the mean, the figures show a
certain parallelism between the total number of bacteria in the crude sewage and the number of
liquefying bacteria, and lastly between the number of spores and liquefiers.
As regards the 4-foot coke-bed effluents there is evidence of a distinct relation between the
total number of bacteria and spores of bacteria, the total number of bacteria and the number of
liquefying bacteria, but little or none between the number of spores and number of liquefiers.
With respect to the 6-foot primary coke-bed effluents there is no definite correspondence
between the total number of bacteria and either the number of spores of bacteria or the number of
liquefiers; and the spores and liquefiers show, if anything, an inverse relation.
It is to be noted that the number of liquefying bacteria was less in the effluents from the
4-foot coke-bed than in the effluents either from the 6-foot primary or 6-foot secondary coke-beds.
The exact value to be placed on the determination of the number of liquefying bacteria is
difficult to judge of. At one time it was thought that the greater the number of liquefying
bacteria in a water the more dangerous was the nature of the contamination, and the more unfit
the water was for domestic use. But as many objectionable bacteria (e.g., B. coli) do not liquefy
gelatine and many pure waters are rich in liquefying microbes of a harmless nature, this test fell
into comparative disfavour. When, however, the character of the liquefying bacteria in the
substance under examination is taken into consideration, the position of things is somewhat altered.
Thus in 14 samples of crude sewage and effluents there were present at least 100,000 gas-forming
"sewage proteus"* per c.c. So that it may safely be said that at least one-tenth of the numerous
liquefying bacteria in sewage are proteus-like in character. And as some of the strains of this
"sewage proteus" isolated from the raw sewage and the effluents were found to be very virulent, it
may be added that crude sewage and effluents from bacterial coke-beds are not only rich in
liquefying bacteria, but that they contain liquefying germs in great abundance which are very
objectionable in kind.
In conclusion it is worthy of note that the ratios of spores and of liquefiers to the total
number of bacteria in the crude sewage and effluents are as follows—
Crude sewage (26 samples)—Ratio of spores (aerobes) to
total number of bacteria = 1 : 21,640
4-foot coke-bed effluent (15 samples)—Ratio of spores
(aerobes) to total number of bacteria = 1 : 19,709
6-foot primary coke-bed effluent (8 samples)—Ratio of
spores (aerobes) to total number of bacteria = 1 : 26,513
6-foot secondary coke-bed effluent (3 samples)—Ratio of
spores (aerobes) to total number of bacteria = 1 : 13,436
Crude sewage (26 samples)—Ratio of liquefiers to total
number of bacteria = 1 : 6'8
4-foot coke-bed effluent (15 samples)—Ratio of liquefiers to
total number of bacteria = 1 : 6-l
6-i'oot primary coke-bed effluent (8 samples)—Ratio of
liquefiers to total number of bacteria = 1 : 8*1
6-foot secondary coke-bed effluent (3 samples)—Ratio of
liquefiers to total number of bacteria = 1 : 5*1
These results would seem to indicate that the result of the bacterial treatment of the raw
sewage in the coke-beds was to effect an increase in the number of spores and of liquefiers relative
to the total number of micro-organisms in the case of the 4-foot and 6-foot secondary beds and to
bring about a decrease in the number of spores and liquefiers relative to the total number in the
case of the 6-foot primary coke-bed. In the Second Report it was stated that the percentage
reduction of spores was greater than the reduction of the total number of micro-organisms in the
4-foot coke-bed effluent as compared with the crude sewage. The figures, however, dealt only
with the period extending from May 9th to August 9th, whereas the above records include as well
hose given in Addenda to the Second Report—i.e., the results obtained between August 9th to
December 31st, 1898.
* This micro-organism is fully described in Section V., Division II., of Second Report.