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50
In summarising these results it is to be noted that—
(1) The number of spores of B. enteritidis sporogenes in the crude sewage and
effluents varied as a rule from 10 to 1,000 per c.c. Usually there were more than 100.
(2) The bacterial treatment did not produce any significant alteration in the number
of spores of this pathogenic anaerobe, and sometimes the number was greater in the effluents
than in the corresponding samples of crude sewage. Possibly this may be due to the spores
being stored in the coke-beds and being occasionally washed out. This supposition
may also explain the observed fact that sometimes the number of spores of aerobic
bacteria in the effluents was greater than in the corresponding sample of sewage.
Speaking generally, and dealing only with the experiments where the samples of raw sewage
and effluent corresponded, and where the absence of B. enteritidis was established in an
amount of liquid one-tenth less than the quantity in which it was found to be present, it
may be said that the number of spores of enteritidis was more often observed to be less in the
effluents as compared with the corresponding sample of crude sewage than vice versa.
In view of these results, and remembering the virulence of this microbe and its probable
relation to certain cases of acute diarrhoea in the human subject, it is remarkable that some
bacteriologists still assert that the effluents from bacterial beds are free from pathogenic germs.
Another point on which some misconception is evident is the belief that because B. enteritidis
sporogenes may be present in normal stools its presence in an effluent or in a water supply is of no
moment. Passing over the fact that its numbers in normal stools are small when compared with the
great numbers which are found in the excreta of patients suffering from acute diarrhoea, it is as idle
to assert that because it may be present in normal stools its presence in an effluent or a water-supply
is of no importance, as it would be to say that because diplococcus pneumoniæ (one of the most
pathogenic micro-organisms known) may be present in normal human saliva, its presence elsewhere in
nature is not fraught with any untoward significance. Moreover, it would seem to be the case that
although the spores of B. enteritidis sporogenes may be found in the large intestine they are usually
absent from the small intestine, except in cases of acute diarrhoea, when they are present in great
abundance.
In the First Report a micro-photograph* is given showing the appearances produced in
sterile milk when inoculated with a minimal quantity of sewage and thereafter heated to 80 °C for
ten minutes and cultivated anaë
robically at blood-heat. Briefly, the casein is precipitated and
torn into irregular masses by the copious development of gas, and the whey presents a nearly
transparent or slightly cloudy appearance. Now, even if we forget that these characteristic
changes in the milk are microbial in origin, and discard altogether the question of the pathogenicity
of the micro-organisms concerned in the process, and regard the change in the medium
merely as a special phenomenon to be associated with the introduction of certain substances as
opposed to others, the test still remains one of extreme value. For the particulate matter in as
much as from 100 to 500 c.c. of a pure water does not in point of fact produce these changes when
added to milk, whereas the addition of as little as to c.c. of sewage does do so. Nor do
we know of any substance which is not objectionable in character or which has not been associated
at some time with matter of undesirable sort which can effect a similar transformation in milk.
The only possible objection that can be urged against the test is that the fact of B. enteritidis
sporogenes being a sporing anaerobe weakens somewhat its usefulness as an indication of
recent and therefore presumably specially dangerous pollution. Of course such a contention has
little or no bearing on the experiments carried out in this inquiry.
It will be noted that the spores of B. enteritidis often exceeded in number the total number
of spores of aerobic bacteria. The reason for this probably lies in the fact of B. enteritidis being
an anaerobe. In nature anaerobic micro-organisms are usually found to be present in the sporeform,
because doubtless it is but seldom that the conditions are favourable for their anaerobic
growth, and if they were not capable of forming spores under adverse circumstances they might
soon lose their vitality and die. Aerobic bacteria, on the other hand, commonly find in nature the
conditions favourable for their continued growth and multiplication, and so are usually met with
in the vegetative form. In surface soil, however, as has been already pointed out, the ratio of
spores to bacteria is very high, because the physical conditions are frequently most unfavourable
to microbial life.
On comparing the figures as regards the total number of bacteria and number of spores of
B. enteritidis no definite correspondence can be made out between the two sets of figures either in
the case of the crude sewage or in the effluents. In not a few cases when the total number of
bacteria was large the number of spores of B. enteritidis was small and vice versa.
It might perhaps have been anticipated that both in the ease of the crude sewage and in
the effluents there would be some measure of correspondence between the number of B. coli and
the number of spores of B. enteritidis sporogenes. On comparing the two sets of figures it would
seem that this is not the case; indeed, if there is any relation at all it is an inverse one. Thus
dealing in the first place with the crude sewage only it will be noted that—
On ten different occasions the number of spores of B. enteritidis was very high, viz., at
least 1,000 per c.c. On the corresponding dates the number of B. coli was five times below the
average, only twice above, and on three occasions there were present the average number.
Taking next the five samples in which B. coli was present in great numbers, namely,
1.000,000 or more per c.c. In the corresponding samples the number of spores of B. enteritidis was
about the average three times, less than the average once, and above the average once.
Taking next three samples in which B. enteritidis was present in small numbers,
namelv, at least 10 but less than 100 per c.c. On one of these dates B. coli was present in numbers
exceeding one million per c.c., and in the two other samples B. coli was below the average.
* Fig. 14—Filtration of Sewage—First Report.