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13
SECTION II.
The comparative bacteriological examination of the water representing the firtt and, final " washings" of
watercress obtained from pure and impure beds.6
The results expressed in terms of B. coli or coli-like microbes in the "washings" of ten grammes,
one gramme, or fractions of a gramme of watercress are set forth in detail in Table II. It is to be noted
that, practically speaking, the results per gramme of cress are comparable with the results per cubic
centimetre of water (Table I.). See page 12.
In summary of the results set forth in Table II., See page 14, the following points deserve
consideration:—
In the first place it is clear that, as judged by the B. coli test and on mathematical lines of comparison,
any danger accruing to the consumer of "unwashed" watercress would be enormously reduced by
careful washing of the cress. It may be objected that my process of washing was, perhaps, more
thorough than could be expected in practice, and that for the final "washings "sterile water was used.
But as regards the former point, I was dealing with a principle, not with the notions of cleanliness of
the average "washer" of watercress, and in respect of the latter point, the biological purity of the
water used for washing purposes has nothing to do with the biological quality of cress, as cress.
Secondly, it is to be noted that even an excess of care devoted to the washing of cress from
polluted sources does not always entirely free the cress from objectionable microbes.
Thirdly, it is apparent from a comparison of Tables I. and II., that there is usually a broad
parallelism between the degree of the impurity of the water and the degree of impurity of the cress
obtained from corresponding localities. At the same time, there is some indication that a cress grown
in polluted water need not always reflect, as it were, its objectionable entourage. It is possible that
the cress from ill-tended and the cress from well-tended beds may exaggerate and "mask" respectively
the biological quality of the surrounding water.
Fourthly, the results show quite conclusively that there may be as remarkable a distinction
biologically between the first ''washings" of the cress from polluted and the first "washings" of the
cress from non-polluted areas as was shown to be the case when the waters derived from pure and
impure localities were compared.
Fifthly, comparing the number of coli-like microbes per gramme of cress (washings) with the
number of coli-like microbes per cubic centimetre of corresponding water, it is apparent that sometimes
the cress and sometimes the water was, of the two, the more impure.
Lastly, it was observed that the results of the first and final washings of the cress usually bore
some relation to each other. For example, the more impure the first " washings," the less effective as
a rule was the washing in removing the objectionable bacteria from the cress.
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 occurs in each case certain letters indicating the biological
characters of the microbe representing the culture. The significance of these letters is explained under
" methods."
SECTION III.
The results, as regards subsequent isolation of B. coli or coli-like microbes, of the addition of cress in definite
quantities directly to liquid culture media both before and also after prolonged washing.
These experiments were undertaken because the "washings" series of experiments, although
dealing with the bacteria adhering to the cress and capable of being detached by a first or final process
of washing, did not show whether or not the stomata or ducts of the leaf or stalk could harbour objectionable
microbes. Obviously, even if the final "washings" of cress were sterile, the cress might still
contain interiorly, or so firmly attached to it exteriorly as to be incapable of being washed away,
undesirable microbes.
The results are set forth in detail in Table III. See page 15.
Generally speaking, it was found more difficult to isolate B. coli from, say, 10 grammes of cress
directly introduced into the culture medium than from the washings of a similar or even smaller quantity
of cress. It is possible that the presence of the cress in the medium may have a slight inhibitory action
on the development of B. coli, whilst not restraining to a like extent the multiplication of other bacteria.
This would account for the difficulty sometimes experienced in isolating B. coli from the secondary plate
cultures.
The results interpreted in a broad and general way indicate that cress grown in polluted waters
both before and even after washing harbours as a rule undesirable 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 case certain letters indicating the biological
characters of the microbe representing the culture. The significance of these letters is exolained under
" methods."
6 Tho question of the possibility of the spread of entozoic diseases by means of watercress lies outside the scope of this
report.