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6. Search for special micro-organisms.
Bacillus Coli Communis.
10 c.c. of sterile gelatine are melted, 0.1 c.c. of 5 per cent. phenol is added, and then the
gelatine is poured into a plate and allowed to become quite solid. From 0.l* to 0.5 c.c. of diluted
sewage (1:10,000) is next added and is spread over the entire surface with a sterile platinum spreader.
Colonies which are typical of Bacillus Coli in their microscopical appearance† and in the manner
of their growth ‡ are then selected, and subcultures are made from them in broth for the observation of
the diffuse cloudiness and the indol reaction, in litmus milk for observation of acidity and clotting, and
in gelatine "shake " for observation of gas production. §
Typhoid bacillus, and Diphtheria bacillus.
The Typhoid bacillus is to be sought for in surface phenol gelatine and in potato gelatine plates,
and the Diphtheria bacillus in ascitic agar plates incubated at 37° C. But the occurrence of these two
micro-organisms in sewage in numbers sufficiently great to afford even a faint hope of their isolation
must be an event so rare that it is probably a waste of time to specially search for them when
more practical and more immediately useful work claims attention.
Staphylococci and Streptococci.
These are to be looked for in agar cultivations incubated at 37° C.
Spores of Bacillus Enteritidis Sporogenes (Klein).
Dr. Klein's method for detecting the spores of this bacillus is as follows. A minute quantity
of sewage is added to 15 c.c. of freshly prepared sterile milk contained in a test tube. The tube is
then heated at 80° C. for ten minutes, cultivated anaerobically by Buchner's method, and incubated
at 37° C.
In the case of London crude sewage the most suitable dilution is 1 in 100, and of this diluted
sewage 1.0, 01, and 0.01 c.c. respectively are added to three of the sterile milk tubes. When B.
Enteritidis is present|| the casein is precipitated, the whey remains nearly colourless, and there is a
marked development of gas. These changes in the milk commonly take place in less than twentyfour
hours. A guinea pig inoculated with 1 c.c. of the whey usually dies in less than twenty-four hours,
and presents, on post-mortem examination, appearances which are typical of enteritidis (extensive
gangrene, sanguineous exudation full of bacilli, etc.).
C.—SUMMARY OF RESULTS SHOWN IN TABLE I.
The results of the bacteriological examination of London crude sewage, which are shown in
Table I., may be summarised briefly as follows—
1. Total number of bacteria.II
The number of micro-organisms present in 1 c.c. of the different samples of sewage varied
as follows—
Barking crude sewage.
7,260.000, highest number, May 3rd, 1898. Experiment 13.
513,333, lowest number, April 15, 1898. Experiment 6.
3,899,259, average of 19 cultures of 9 samples. Experiments 2, 5, 6, 7, 9, 10, 12, 13
and 14.
Crossness crude sewage.
5,290,000, highest number, March 2nd, 1898. Experiment 4.
2,410,000, lowest number, April 20th, 1898. Experiment 8.
3,526,667, average of 11 cultures of 6 samples. Experiments 1, 3, 4, 8, 11 and 15.
Barking sewage contained on an average nearly four million and Crossness three and a half
million bacteria per c.c. It is evident that the various substances, such as waste matters from manufactories,
which are discharged in large quantities into the London sewers, and yet may be regarded
as foreign to sewage, do not inhibit the growth of the sewage bacteria to any marked extent.
The above figures refer to the number of spores of bacteria actually present in sewage, and
must not be considered as meaning the number of bacteria capable of forming spores.
2. Number of spores of bacteria.
The number of spores of bacteria present in 1 c.c. of the different samples of sewage varied
as follows—
Barking crude sewage.
30,000, highest number, February 23rd, 1898. Experiment 2.
80, lowest number, April 4th, 1898. Experiment 5.
3,899, average of 15 cultures of 9 samples. Experiments 2, 5, 6, 7, 9, 10, 12, 13
and 14.
* See No. 1 (Plate I.). † See No. 6 (Plate I.).
‡ See Nos. 1, 4 and 13 (Plate I.). § See No. 5 (Plate I.).
|| See No. 14 (Plate I.;.
¶ See No. 2 (Plate I.), as illustrating the number of bacteria in sewage.