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In such a sample as this, one would be guided by the relative number of such orga-
nisms as lactis ærogenes. It has been shown that, in the ordinary fresh mixtures
of faces and water, laotis æ rogenes is not particularly common. Therefore a water
showing a mixture, rich in varieties, and yet containing few or no lactis ærogenes,
would be judged to have undergone very little settlement or purification.
If, on the other hand, one found the sample containing faecal organisms in
1 cc., showing only 2 or 3 varieties, one of which belonged to class III, and if the
predominating organisms happened. to be lactis ærogenes, this would constitute fairly
satisfactory evidence, that a considerable amount of purification had gone on since the
fœ cal matter was actually added to the water. The work given in chapters IX and X
shows conclusively that, in all waters stored for some time, lactic ærogenes is a
common organism, and that it is not so, in newly contaminated waters, or in waters
stored for many months.
This may be taken as the rough idea as to how conclusions can be arrived at
in the types of results commonly met with. On the subject of numerical standards,
no hard and fast rules can ever be laid down, and a considerable amount of latitude
must always be left to the discretion of the analyst. In the above remarks it is
presumed that besides the actual organisms found in each sample, the number of lactose
fermenting organisms per cc., and the total colonies in .1 cc., are taken into consid-
eration. The results obtained in the bile salt broth tubes are also very important.
Thus, practically any water in India that contains no foetal bacilli in 20 cc. is probably
a good water (provided of course none of class I are obtained in a large amount).
A few actual examples of the various classes of results will be found at the end
of this chapter for reference.
We now come to the consideration of waters that have not been exposed to the
s u n , v i z . , t h o s e d e r i v e d f r o m w e l l s a n d s p r i n g s . P r o b a b l y t h e g r e a t e s t o b j e c t i o n t o t h e
method tha t we propose is, we do not know how far it applies to waters from such
suffices. The question is much more complicated than those met in dealing with
surface waters, the difficulties being (i) to estimate the importance and signi-
ficance of organisms that remain alive in the soil for long periods, and (ii) to be quite
certain when a pollution is caused by surface contamination, washed downwards
through cracks or through a porous soil. In dealing with well waters the great point
to look to is the quantity of fatal pollution. Of course when col i c communi s i s i tsel f
present, with a mixture of other organisms, there can be no doubt, that contamination
of a dangerous nature has taken place. But when, as is so often the case, most of the
bacilli present consist of a mixture of class II, with probably a few of class III, how far
is it safe to assume that this type of pollution is not serious? It would not be wise
to place much importance on the power of resistance of the organisms present, for in
well waters we are not dealing with the resistant majority, but with the whole lot
resistant and susceptible alike. An example of the difficulty referred to above is to be
found illustrated in the result obtained from tire King Institute well—xide Chapter VI.
Not infrequently, a well water, in normal hot weather condition, containing only one
organism, and that a resistant one, will, with comparatively slight meteorological
changes, suddenly be found to contain a very large number of colic communis. We
are at present in absolute ignorance, both as to whe'e these organisms come from (for
they certainly do not come from recent surface pollution), and also as to what is their
precise significance. They cannot be looked upon as altogether harmless, because,
supposing our theory is correct, that these organisms remain alive in the damper
layers of soil, there is no certainty that the organisms of enteric and cholera may
not do so as well. Consequently one is bound to regard their presence with great
suspicion. On the other hand, in what may be termed the hot weather condition of
wells and springs, bacillus cloacæ is nearly always the only organism present, and,
knowing as we do, that this bacillus is gifted with great longevity in soil, no very
great significance can apply to s presence of these organisms, provided that the
number is not too large. We can only therefore advise as follows, (1) look with
grave suspicion on all faecal bacilli in well water, (2 be guided more by the quantity
of fœcal organisms per cc. than by the kind. of organisms; and (3) on no account ever
give an opinion without an inspection of, or a report on the surroundings by a medical
officer. It should be borne in mind that extremely valuable information, as to the