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57
Excluding the results obtained on January 11th, as the figures are abnormally high, and
there is no record on that date for the 6-foot secondary coke-bed, the averages are as follows—
Average number of spores of anaërobic bacteria in five samples of Crossness crude sewage, and
in five comparative effluents from the 4-foot, 6-foot (primary), and 6-foot (secondary) coke-beds, 268;
267; 240; and 207 per c.c. respectively.
It will be seen from these results that the bacterial treatment of the crude sewage in the
coke-beds did not effect any marked alteration in the number of spores of anaerobic bacteria. Indeed
the number in the effluent from the 4-foot coke-bed was practically the same as in the raw sewage, and
in the case of the effluents from the 6-foot (primary) and 6-foot (secondary) coke-beds the reduction
was only 10 and 22 per cent. respectively.
Pressure of other work for the Council made it impossible to study fully the morphological
and biological characters of the different kinds of anaerobic bacteria isolated in pure culture from the
anaërobic agar plates; and the notes under this heading are of too fragmentary a character to make
it advisable to place them on record. So far as could be made out there was no difference as regards
species of microbes between the anaerobic cultures made from the crude sewage and those made from
the effluents from the coke-beds.
The appearance presented by the colonies (superficial and deep) under a low power of the
microscope is shown diagrammatically in Plate V., fig. C. So far as could be judged by observation
under a low power of the microscope and by making sub-cultures the number of spore-forming
anaerobes of different species was not great. As regards growth in anaerobic milk culture some of the
microbes isolated from the agar plate cultures produced precipitation of the casein, with abundant
development of gas, the whey remaining nearly transparent, or presenting only a slightly cloudy
appearance; others produced no visible change even after several days incubation at 37° C.;
others again gave rise to an appearance resembling slow peptonization, beginning just below the
surface, and gradually extending downwards in cylindrical fashion.
A rise or fall above or below the mean in the number of the spores of anaerobic bacteria in the
crude sewage was usually associated with a similar increase or decrease in the number of spores of
anaerobes in the effluents from the 4-foot, 6-foot (primary), and 6-foot (secondary) coke-beds.
In conclusion, and as an addition to the records of the bacterial composition of Crossness
crude sewage, it may be worthy of note that the number of spores of anaerobic bacteria (agar at
37° C.) in Crossness crude sewage is usually between 200 and 300 per c.c.
2.—EXPERIMENTS WITH THE EFFLUENTS FROM THE 13-FOOT COKE-BED AT
CROSSNESS*
The chief results obtained will be given under the following headings—
(a) Total number of bacteria (gelatine at 20° C.).
(b) Number of B. coli or closely allied forms.
(c) Number of spores of B. enteritidis sporogenes (Klein).
(d) Number of bacteria capable of growing in agar at 37° C.
(a) Total Number of Bacteria (gelatine at 20° C.).

These results are shown in graphic form in Diagram 6.
It is to be noted that the average numbers of microbes in the crude sewage and in the
effluent from the 13-foot coke-bed were 5,711,000 and 5,364,000 per c.c. respectively. This means
a reduction of only 6 per cent., the reason being that on July 5th and August 2nd the effluent contained
a much larger number of micro-organisms than the raw sewage. On all other occasions,
with one exception (October 4th), the effluent contained fewer bacteria than the corresponding
samples of crude sewage. A rise or fall above or below the mean in the total number of microbes
in the raw sewage was coincident with a similar increase or decrease in the number of germs in the
corresponding samples of effluent on eight occasions. In the remaining three cases this relationship
was not observed.
* A description of this bed will be found in the Chemical Division of the Report.
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