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59
The following Table gives the number of bacteria (agar at 37° C.) in Crossness crude sewage
and in the effluent from the 13-foot coke-bed. It also gives, for comparative purposes, the number
of bacteria (gelatine at 20° C.) in the corresponding samples.

These results are shown in graphic form in Diagram 9.
The Table shows that the average number of bacteria (agar at 37° C.) in the crude sewage
and in the effluent was 3,294,444 and 2,802,857 respectively per c.c., showing a reduction of about 14
per cent. Further, that the average number of bacteria (gelatine at 20° C.) in the crude sewage and in
the effluents was 5,758,571 and 4,662,857 respectively per c.c., i.e., a reduction of about 19 per cent.
Comparing the figures 3,294,444 (agar at 37° C.) and 5,758,571 (gelatine at 20° C.) it is to
be noted that the difference is 42 per cent., hence more than one-half of the number of bacteria
capable of growing in gelatine at 20° C. can likewise grow in agar at 37° C. When a similar
comparison is made as regards the effluents from the 13-foot coke-bed the difference is 39 per cent.
It is evident from these results that the bacterial treatment of the sewage in the coke-beds did
not effect any marked reduction in the number of blood-heat organisms; indeed, the reduction was
less as regards these germs than as regards the bacteria growing in gelatine at 20° C.
Although gelatine is doubtless a more favourable medium than agar for the growth of bacteria
of all sorts, it is not the difference of nutrient medium, but of temperature which chiefly accounts
for the difference in the numbers under the two sets of conditions. As a matter of fact the number
of bacteria in sewage capable of growing at 37° C. is both actually very great and is very great also
in relation to the total number of microbes growing at the ordinary temperature, the reason
apparently being that so many of the micro-organisms found in sewage are derived from the
intestinal discharges of animals, e.g., B. coli, which has been shown to be present in numbers
usually exceeding 100,000 per c.c.
In pure waters the number of "blood-heat" bacteria is usually small, and their ratio to
the number of germs growing at the ordinary temperature is likewise small.
Although a large number of "blood-heat bacteria is considered a bad sign, it must not
be supposed that all the different species of microbes capable of growing at 37° C. are harmful.
Many found in sewage and elsewhere in nature are, so far as we know, quite unobjectionable, e.g.,
B. subtilis, B. mesentericus, B. mycoides, etc. On the other hand others are decidedly objectionable
and may be pathogenic, e.g. B. coli and B. proteus (certain forms), and some are definitely
pathogenic, e.g., B. pyocyaneus. In the Second Report (page 27) it was stated—"A cultivation of
B. pyocyaneus isolated from a sample of Crossness crude sewage proved to be extremely virulent.
Thus 1 c.c. of a twenty-four hours' broth culture (at 37° C.) injected subcutaneously into a guineapig
killed the animal in less than twenty-four hours, and the organism was recovered in pure
culture from the heart's blood, spleen, etc."
On November 1, 1899, B. pyocyaneus* was isolated from 1/1000 c.c. of the effluent from the
secondary coarse bed (series A) at Barking. A guinea-pig injected subcutaneously with 1 c.c of a
twenty-four hours' broth culture (at 37° C.) died in less than twenty-four hours, and the same
micro-organism was isolated in pure culture from its heart's blood.
In the light of this result (apart from the numerous records contained in this and previous
Reports of equal or greater significance) it is strange that many still consider the effluents from
coke-beds and in general from bacterial processes, non-pathogenic.
So far as may be judged by a rise or fall above or below the mean, the figures show that both
as regards the crude sewage and the effluents there was a decided parallelism between the number
of bacteria growing in agar at 37° C. and the number growing in gelatine at 20° C. Similarly, a
rise or fall above or below the mean in the number of bacteria capable of growing in agar at 37° C.
in the crude sewage was nearly always coincident with a rise or fall in the number of microbes in
the corresponding effluents from the 13-foot coke bed.
In conclusion, and by way of addition to the chief results which have been obtained during
the progress of the inquiry, it is to be noted that the number of bacteria capable of growing in
agar at blood-heat in Crossness crude sewage is usually over three millions per c.c., and more than
one-half of the number of microbes growing in gelatine at 20° C. It must be admitted that the
13-foot coke-bed at Crossness yielded very unsatisfactory results from the bacteriological point of view.
* See fig. 5.