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SECTION IV.
Comparative examinations bacteriologically of the leaf and stalk of watercress.
These experiments were undertaken because it might be asserted that as it is the leaf of the cress
that is largely eaten, the inclusion of any greater proportion of the stalk in the quantitative analyses
than is likely to be consumed in practice is not quite fair.7 A strict comparison of the bacterial flora
of the leaf and stalk of cress would be a most difficult task. A broad comparison only can be attempted
here.
The results are shown in detail in Table IV.
It is quite clear from the results that both the stalk and leaf of cress may harbour objectionable
microbes.
As regards the biological attributes of the B. coli or coli-like microbes isolated from the cultures,
it is to be noted that above the sign+there occur in each instance certain letters indicating the biological
characters of the microbe representing the culture. The significance of these letters is explained under
"Methods."

* The significance of these letters is described under "methods."
SECTION V.
The question of standards.
This subject is one of such grave importance to the watercress industry that it is felt that at the
present time only tentative suggestions should be made. It is difficult to decide whether or not any
standards, provisional or otherwise, should be of a two-fold character. That is, whether they should
take note of the biological quality both of the water and the cress. Inasmuch as, generally speaking,
the results show that the cress is apt to reflect bacteriologically its aqueous environment, there would
seem to be an advantage in reducing the question to one of water. Whether the affluent, circumfluent,
or effluent waters should be chosen for investigation is matter for conjecture." On the whole, perhaps,
the examination of the affluent water should form the basis for judgment.
Strictly speaking, drinking water standards are applicable to the water "feeding" watercress
beds. But the imposition of such standards would press, it is to be feared, rather heavily on the watercress
industry. The responsibility of correlating the bacteriological and chemical facts and topographical
observations with epidemiological experience must rest with the administrator. In this connection
the following observations may be of some value.
In the first place it is noteworthy that the best samples of water (VII., VIII., XII. and XIII.) were
ten million times purer bacteriologically than the worst samples of water (III. and XI.), and one million
times purer bacteriologically than samples II., IV. and X. This per se affords a reasonable and definite
basis for objecting to the worst cases of pollution. Yet these cases, it may be contended, hardly need
the confirmatory evidence of the bacteriologist. When we step inside a narrower circle the bacteriological
facts remain none the less definite, but their interpretation in relation to potential danger to health is apt
to grow more nebulous. Not, perhaps, on a purely mathematical basis, but from an added sense of
responsibility, and an increased conviction that the bacteriological facts afford no direct indication
of the "disease value" of a given pollution.
Secondly, treading on safer ground, it may be said that it is desirable that all watercress
beds should, on the basis of the biological qualities of their affluent waters, be divided into separate
classes. This does not involve necessarily the question of bacteriological standards or of legislative
condemnation. It merely means that the affluent waters to all watercress beds should be classified.
It is not suggested that the bacteriological results should be used necessarily as a lever for condemnatory
purposes, but rather that a bacteriological classification would, particularly when coupled with the
7 That is, on the assumption that per gramme of weight the stalk would be more impure than the leaf. This point,
however, has yet to be established.
8 The affluent, circumfluent and effluent waters are the waters "feeding," flowing round the watercress, and leaving
the watercress beds respectively.