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17
observations of the chemist and topographist, aid the administrator in a progressive attempt to remedy
pressing evils. In this sense, and with the modifications which the circumstances of the case demand,
I would suggest a broad classification on the lines already tentatively brought forward in reports to the
Local Government Board and Royal Commission on Sewage Disposal, as follows:—
CI.ASS.*
Standard based on numerical
abundance of B. coli (or nonliquefying,
gas-forming coli-like
microbes).
Numerical standard confirmed
or modified according to
response of the coli-like
microbes in pure culture to certain
well-known biological tests.
Provisional bacteriological
conclusions confirmed
or modified by topographical
observations.
Provisional bacteriological
& topographical conclusions
confirmed or modified by
epidemiological & administrative
considerations.
I.
A water showing no evidence
(bacteriologically)
of objectionable contamination
No B. coli in 100 c.c.
For example:—
(1) Neutral-red broth test—
Greenish-yellow fluorescence
(48 hrs. at 37° C.)
For example:—
Degree of cleanliness
of watercress beds.
Source and probable
nature of the pollution
and its proximity
to the beds. Local
arrangements for
washing the cress in
pure water before
being dispatched to
market. Relative
volumes of the
different waters
"feeding" the beds,
etc.
For example:—
Questions of practicability
; whether the
contaminating material
is likely to have
a high or a low enteric
morbific value; past
epidemiological experience
in circumstances
broadly
parallel, etc., etc.
II.
A water showing appreciable,
although slight,
evidence (bacteriologically)
of objectionable
contamination
B. coli present in 100 c.c.,
none in 10 c.c.
(2) Lactose peptone test—
Gas and acid production
(48 hrs. at 37° C.)
(3) Indol test—Indol in
broth cultures (5 days at
37° C.)
III.
A water showing definite
signs (bacteriologically) of
pollution, and therefore to
be viewed with some
degree of suspicion
B. coli present in 10 c.c.,
none in 1 c.c,
(4) Litmus milk test—Acid
clotting of milk (5 days at
37° C.)
Of course, the more tests
applied the better, but the
above are all tests of
known value.
IV.
A water showing such obvious
signs (bacteriologically)
of objectionable pollution
as to be condemned†
on the basis of results
B. coli present in 1 c.c.,
none in 0.1 c.c. (1 not 10)
[4s regards tests (1), (2), (3)
and (4), my work for the
Local Government Board
on the B. coli of recentlyvoided
normal human
faeces shows that of 101 B.
coli, 98, 92, 98 and 92 per
cent. respectively yielded
positive results to one or
other test. As regards all
four tests (taken in conjunction),
85 per cent.
yielded positive results.]
V.
B. coli present in 0.1 c.c.
None in 0.01 c.c. (10 not
100)
VI.
B. coli present in 0.01 c.c.,
none in 0.001 c.c. (100 not
1000). [Primary standard
for sewage effluents; nondrinking-water
streams]
VII.
B. coli present in 0.001 c.c.,
none in 0.0001 c.c. (1000
not 10,000). [Secondary
standards for sewage effluents;
non-drinking-water
streams.
* It must, of course, be definitely understood that I am not prepared to say that a water of Class III., II., or even I. is necessarily
always "safe," much less that a water of Class IV.—VII. has a definite "disease value."
† This does not mean necessarily administrative practical or legislative condemnation, but rather that the evidence of pollution is
sufficiently defined to merit objection from the bacteriologist's point of view. [This standard is intended to apply primarily only to
potable waters.]
N.B.—The B. enteriditis sporogenes test is not dealt with here. Perhaps the safest standard to suggest is that a water should yield a
negative result when using 10 c.c. for cultural purposes. [This standard is intended to apply primarily only to potable waters.]
SECTION VL
Summary and condusions.
The best waters contained no coli-like microbes of any sort, and no spores of B. enteritidis sporogenes
when 100 c.c. and 10 c.c. respectively were used for cultural purposes.
The least satisfactory waters contained from 1,000 to 10,000 B. coli or coli-like microbes per c.c.
and yielded positive results with the B. enteritidis sporogenes test with from 1/10th to 1/100th of a cubic
centimetre.
On the basis of the B. coli test the best waters were from one million to ten million times
purer than the least satisfactory waters.
Generally speaking, watercress reflects bacteriologically its aqueous environment. That is, the
more polluted the water the less pure is the cress, and the purer the water the cleaner is likely to be the
cress. But the results were sometimes (partly, perhaps, for technical reasons) inconclusive and not in
entire correspondence. It is possible that cress grown in well tended beds may escape in some measure
the contamination by an impure circumfluent water.
The importance of thoroughly washing watercress is shown by the fact that the final as compared
with the first " washings " of impure cress was usually found to contain a much smaller proportion of
objectionable microbes.
But the results seem to indicate that no ordinary amount of washing could be relied on to rid cress
grown in polluted waters of all undesirable microbes. This may be due either to bacteria so firmly adhering
to the exterior of the plant as to resist being swept away during the washing process, or to the
cress harbouring microbes within its structure, or to a combination of these causes.
The results appear to prove that both the leaf and the stalk of cress may foster undesirable
bacteria.
4058] C