73
in 100, or 1 in 50 cc. But even admitting this objection, it will be observed, that
out of 12 different water-supplies examined, either cloacæ, or grunthal, or both, were
present in 11, and greatly predominated in no less than S. The extraordinary
n u m e r i - c a l p r e d o m i n a n c e o f t h e s e o r g a n i s m s o v e r a l l o t h e r s , m a y b e t a k e n t o b e v e r y s t r o n g
evidence in favour of the truth of the statement, that these organisms are resistant to
the action of sunlight and storage.
Coli communis was isolated once in this quarter, from the Marlimund reservoir
in Ootacamund. Inspection has shown that the catchment area was contaminated
to a considerable extent by wood-cutters, in the immediate neighbourhood of the lake,
and that light rain was actually falling at the time when sample was taken. Coli
communis was entirely absent from all other samples.
Second quarter.—A. very marked difference has come over the results of the
analyses of samples taken during the quarter ending 31st December 1908. First of
all, there has been a great improvement in the average quality of the waters. An
approximate average for this quarter is 1 fœcal organism in S cc. of water. In
no less than 6 out of 13 samples, fœcal bacilli. were only present in 5 cc. or more.
But the most important change that is observed between the first and the second
quarter is best shown by table X (b). The large falling off in the number of bacillus
cloacæ and grunthal is apparent. The great increase in organisms, which may be
termed, those of medium powers of resistance, is also extremely marked. Organisms
such as lactis ærogenes coscoroba and No. 67 have increased in number to a very
great extent. Bacillus cloacae and grunthal also persist, but only in very much the
same proportion as they are found in all recently polluted surface waters—vide the
figure for River Waters in table XIII (a). It will also be noticed, that, as compared
with the samples of the previous quarter a mixture of varieties of organisms, is the
general rule.
Coli communis were found in one case namely in the lake at Adoni. The
explanation of this cannot be given satisfactorily, but it is probably due either to
contamination at the edge, or to the fact that the supply stream was still flowing.
Third quarter.—The striking feature about the samples, taken during this
-.quarter, is the great purity of the waters. The approximate average in the samples
is 1 fœcal organism per 40 cc. of the water. The reason for this is obvious, namely,
that during this quarter, the large volume of water, which filled up the lakes, during
the rains of October, November, December and the first week of January, has had ample
time to get thoroughly well sunned, settled and stored. The consequence is, that, in
no less than 4 instances out of 12, fœcal bacilli could only be found in more than 50 cc.
In no case were samples obtained which contained more than one feal organism per
cc. In comparing this quarter with the last the percentage prevalence of organisms
presents little change. The organisms of medium powers of resistance still preponder-
ate very largely. Lactis ærogenes and coscoroba are fairly plentiful. Cloaae has fallen
off to an extraordinary extent ; this is undoubtedly due to the tendency for these
organisms to remain at the bottom of lakes, as has been demonstrated in Chapter IX.
Bacillus grunthal is not common. It is obviously out-numbered by such organisms
as lactis ærogenes and coscoroba. But looking at the organisms common in this
quarter, there is a decided tendency for the more resistant ones in this class to
increase in number—vide the increase of organisms Nos. 73 and 67. It would not
however be wise, at this stage of our knowledge, to lay too much stress on these
minor points of detail ; especially as our method of analyses, when dealing with very
pure waters, has a tendency to increase the percentage of any particular organisms
present. No coli communis were found in the analyses of this quarter.
The study of the results of the analyses obtained side by side with the
prevaiing meteorological condition, demonstrates the extraordinary efficiency of these
natural forces in getting rid of all but the most resistant elements of a pollution,
that is very great in amount at certain times of the year.
Before closing this chapter it may be well to say a few words about the
purity of water on the general health of the inhabitants of the country. It will be
shown later on, that the worst months for cholera, dysentery and diarrhœa are those of
August, September and October ; and the best are those of December, January and
February. It would not perhaps be expected, that the former period of the year, when
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