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11
SECTION I.
Results of the bacteriological examination of the water in connection with watercress beds.
The results of the bacteriological examination of the samples of water collected either from the
watercress beds or in connection with them are set forth in Table I.
It is to be noted that the local conditions were found to be eminently satisfactory in connection
with samples VI., VII., VIII., XII., and XIII. All the other samples (I., II. III. IV., V., IX.,
X., XI.) were obtained from situations considered unsatisfactory, in some cases highly unsatisfactory,
as the result of local inspection.
B. Coli Test.
As judged by the total number of coli-like microbes, the two worst samples (III. and XI.) contained
10,000 coli-like microbes per c.c. (Water of the VIII. class.)3
Three samples (II., IV. and X.) contained 1,000 coli-like microbes per c.c. (Water of the Vll. class).
Two samples (V. and IX.), contained 10 coli-like microbes per c.c. (Water of the V. class).
One sample (I.) contained coli-like microbes in 10 c.c. but not in 1 c.c. (Water of the III. class).
One sample (VI.) contained coli-like microbes in 100 c.c., but not in 10 c.c. (Water of the II.
class)
Four samples VII., VIII., XII., XIII.), contained no coli-like microbes even in 100 c.c.
(Water of the I. class).
Reviewing the results as a whole, there can be no question that with the notable exception of
samples VI., VII., VIII., XII., and XIII. (possibly also sample I.), all the waters were outside the pale
of recognition as judged by drinking water standards. Samples II., III., IV., X. and XI., indeed,
resembled sewage effluents, bacteriologically.
Great stress should be laid on the negative results afforded by the bacteriological examination of
samples VII., VIII., XII. and XIII. It has been asserted that impure water is advantageous, if not
necessary, for the successful cultivation of marketable cress. Yet cress grown in water of the greatest
purity commands justly a ready sale. On the basis of the B. coli test, samples VII., VIII., XII. and
XIII. were at least ten million times purer (bacteriologically) than samples III. and XI., and at least one
million times purer (bacteriologically) than samples II., IV. and X.4
Preventive medicine is based largely on recognition of the importance of presumptive evidence.
The bacteriologist can do no more than present his facts affording evidence of the numerical abundance
of objectionable microbes in such a way as to allow the administrator to measure the relative value of
such facts and by correlating them with topographical observations and epidemiological considerations
to form a reasonable estimate of the degree of potential danger to health.
As regards the biological attributes of the coli-like microbes, it will be noticed that above each
sign † there are certain letters indicating the biological characters of the microbe representing the
cultures. The significance of these letters is explained under " methods."
B. Enteritidis Sporogenes Test.
Two samples (II. and IV.) gave a positive result with .01 c.c.
Two samples (III. and XI.) gave a positive result with .1 c.c.
One sample (X.) gave a positive result with 1 c.c.
Three samples (I., V. and IX.) gave a positive result with 10 c.c.
Five samples (VI., VII., VIII., XII. and XIII.) gave a negative result with 10 c.c.
With the exception of VI., Vll., VIII., XII., and Xill., all the samples would, I think, be
condemned on bacteriological grounds and on a drinking water basis.5 Samples II., III., IV., and
XI. failed to pass my primary standard for sewage effluents.
Streptococcus Test.
As regards samples I., VI., VII., VIII., IX., X., XI., XII., and XIII., either no microbes
resembling in any way streptococci, or no microbes indubitably belonging to the streptococcus class
were found in 0.1 c.c. of the respective waters.
In respect of samples II., III., IV., and V., the diagnosis was uncertain. In all these samples
there were present, in greater or less number, microbes concerning which I was left in much doubt even
after a careful study of their morphological and biological characters. I could not, in brief, come to a
final decision whether or not these microbes should be classed as streptococci of human faecal origin,
nor indeed was I wholly convinced that they merited inclusion in the streptococcus group.
As judged by the streptococcus test, the waters seemed less objectionable than was to be
anticipated from the results of the B. coli and B. enteritidis sporogenes tests.
Nevertheless, there are technical and other difficulties in connection with the streptococcus test
which cause the observer to hesitate to pronounce too dogmatic an opinion.
3 That is, on the numerical abundance of coli-like microbes irrespective of their biological attributes not necessarily
on the " flaginac," B. coli basis. Subject to fulfilment of positive confirmatory tests and considered on the basis
of drinking water, ali the samples except VI , VII. and VIII. (possibly also I.) would be condemned without
hesitation on bacteriological grounds. Samples II., III., IV., X. and XI. failed to pass my primary standard
for sewage effluents. See page 107 et seq. of my report to the Royal Sewage Commission (Fourth Beport,
Volume III.).
4 These are mathematical and biological distinctions. The measurement of the " disease value " of a given pollution
unfortunately cannot be estimated by the topographist, epidemiologist, nor bacteriologist.
6 It is doubtful if drinking water standards could be applied to the water feeding watercress beds without serious injury
to trade. Nevertheless, with the exception of VI., VII., VIII., XII. and XIII., all the samples submitted to me
for bacterioscopic analysis were obtained from beds which, I am informed, could not on topographical grounds be
considered as other than unsatisfactory.
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