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It is to be noted that on three separate occasions the number of B. coli in the crude sewage exceeded
the number found in the 4-foot coke-bed effluent, and on three other occasions the conditions were reversed
in this respect. In the two comparative experiments remaining the numbers were approximately equal.
As regards the 6-foot coke-bed effluent, on one occasion the number in the effluent was somewhat
greater than the number in the crude sewage; on the other occasion the crude sewage contained a much
larger number.
Judging the experiments as a whole it cannot be said that the biological processes at work in the
coke-beds effected any marked alteration in the number of B. coli. It must not, however, be too lightly
considered that this implies that the effluent was necessarily of an offensive and putrescible character.
B. coli and other putrefactive bacteria no doubt work in the direction of purifying the sewage, and their
presence in the effluent might only mean that the purification had not been carried sufficiently far to allow
of a decrease in their numbers, owing to the incomplete reduction of the organic matters on which they
feed and which allow of their continued multiplication. Yet, when this has been said, it must also be
admitted that the passage of an aerobic non-spore-forming bacillus typical of excremental matters through
the coke-beds, in practically unaltered numbers, is not a desirable state of things. It is true that B. coli is
not pathogenic in the ordinary meaning of the word, but its presence in the effluents implies the possible
presence of other bacteria—it might be of dangerous sort. Still, on the whole it may be said that the
balance of evidence points to pathogenic aerobic bacteria being liable to be crowded out in the struggle for
existence in a nutrient fluid containing a mixed bacterial flora and one rich in saprophytic micro-organisms.*
Lastly, it must be remembered that the effluent is discharged into a large tidal river at a point far below
the lowest "intake" of water for waterworks purposes. Moreover, the Thames before it reaches the
Outfalls of the Sewage Works is already grossly polluted with excremental matters.†
In searching for B. coli in the crude sewage and in the effluents the following plan was adopted‡—10 c.c.
of sterile gelatine, contained in a test tube, were melted, 01 c.c. of five per cent. phenol added, and then the
gelatine was poured into a Petri's capsule and allowed to become quite solid. 01 c.c. of diluted sewage, or else
of effluent (1:10,000) was next added and spread over the entire surface of the gelatine with a platinum spreader.
Colonies which were typical of B. coli in their microscopical appearance and in the manner of their growth were
then subcultured in broth (for diffuse cloudiness and indol reaction), in litmus milk (for acidity and clotting), and
in gelatine shake culture (for gas formation). It was not, however, found possible in all of the experiments to
apply all of these tests, although, in the majority of cases the gas test in gelatine was applied.
(c) Other Species of Bacteria.
Besides searching for B. enteritidis and B. coli the attempt was also made to estimate the number
as well as the character of other microbes present in the crude sewage and in the effluents. Notes under
this heading will be found in col. 5 of Table I. Thus the organism called "sewage proteus," of which a
description appears in this report, was found to be present in great numbers (usually over 100,000 per c.c.)
in both the crude sewage and in the effluents. Other microbes found in the crude sewage and effluents
were B. fluoresceins liquefaciens and its varieties, B. fluorescens non-liquefaciens, B. mescntericus (a description
of two varieties of this bacillus is given in this report), B. sublitis, B. mycoides, B. pyocyaneus.§
streptococci, staphylococci, Ac.
In experiments 3 and 5 (col. 5, Table I.) the number of bacteria in the crude sewage capable of
growing at 37° C. in agar was estimated. The numbers were 1,260,000 and 1,171,000 per c.c. as compared
with 3,670,000 and 6,400,000 obtained by gelatine plate cultivation at 20° C. A similar experiment
(experiment 4) with the effluent from the 4-foot filter bed gave 1,630,000 (agar, at 37° C.) as compared with
4,100,000 (gelatine, at 20° C.) bacteria per c.c.
In experiments 9 and 10 (col. 5, Table I.) it was sought to discover the smallest amount of crud
sewage and of effluent which in broth cultures at 20° C. would produce growth, indol reaction and
offensive smell. No growth occurred in either case, when as little as 0.0000001 c.c. was inoculated into
the broth; but when 0.000001 c.c. was used, growth occurred both in the case of the crude sewage and of
the effluent, and the cultures had an offensive smell and gave indol reaction.
In concluding this section of the report it may be said that when making comparative cultivations
from different liquids the trained observer can often detect differences in the characters of the colonies
developing in the nutrient media which are none the less real because they cannot always be put into
definite language. Speaking from this point of view, it must be admitted that little or no real distinction
could be made out between the cultures made from the crude sewage and those made from the effluents,
other than those points of difference already considered—namely, a slight reduction in the total number of
aerobic bacteria, the number of spores of aerobic bacteria, and the number of liquefying aerobic bacteria
found in the effluent, as compared with the crude sewage.
* See, however, notes under heading—The biological treatment of sewage.
t See results shown in Table II. ‡See pages 3 and 6 of First Report.
§ A cultivation of B. pyocyaneus isolated from a sample of Crossness crude sewage proved to be extremely
virulent. Thus 1 c.c. of a 24 hours' broth culture (at 37° C.) injected subcutaneously into a guinea-pig, killed the
animal in less than 24 hours, and the organism was recovered in pure culture from the heart's blood, spleen, &c.