15
The weak point of the above method lies in the statement that a large number of
what we believe to be entirely different species of bacilli. equally represent dangerous
fœcal contamination . If this be so, it should be demonstrable that, these different species
are equally resistant to such forces of nature as the action of sunlight and the action of
storage. Otherwise if it can be proved that one organism is particularly resistant, and
another particularly susceptible to these natural forces, it is obvious that the resistant
organisms cannot be considered, on all occasions, of equal value, as an index of recent
and dangerous pollution, as the susceptible one. Examining the ten organisms, which
fall under Houston's definition of “ coli,” and which represent his worst type of pollu-
tion, we are prepared to state from actual experiments, that, the greatest possible
variation exists in these ten organisms in their power of resistance to the action of natural
forces. To take two extreme examples B. Grunthal is particularly resistant to the
action of sunlight. It is found in waters that have been exposed to the tropical sun
for weeks ; it is nearly always one of the last bacilli to disappear from a well-sunned and
stored water, and also from a mixture of cowdung and water exposed to the sun. On
the other hand, true B. coli communis of Escherrch (the organism that ferments dulcit
and does not ferment saceharose, adonit, inulin, etc.), will disappear with great rapidity
from a water exposed to the action of tropical sun. It is seldom found to survive
longer than three days in a clear water of considerable depth. Is it reasonable to
include both these bacilli under the same term of "true coli," and to state that both
equally represent objectionable pollution? It is possible to elaborate this still further.
In the course of our work we have found that under very exceptional circumstances, a
bacillus known as Oxytocus perniciosus is occasionally found in a water-supply.
There is good reason to believe that this organism is extremely sup ceptible to natural
conditions, such as sunlight, etc., for although it is present in cowdung, and probably
in human fœces, it has only been found in water-supplies after heavy floods, and it
disappears with exti aordinary rapidity. Thus it is probable that this organism repre-
sents a more recent, and therefore a more objectionable contamination, than any other
organism met with up to now. Yet it will be observed that this particular bacillus
does not fall with in Houston's definition of " true coli ", nor within the category of
organism in which according to Savage are " equally of excretal origin." In order
to demonstrate what is exactly meant by this last paragraph, reference should be made
to the analysis of the water of the District Jail of Tanjore, page 345.
The water contains fœ cal baci l l i i n · 01 cc. I t cont ai ns s por ogenes i n 20 cc. and
the total colonies in 1 cc. at 37° were 2,520. The only bacillus that would fulfil the defi-
nition of " coli " according to Houston is B. Grunthal, an organism which we know
to be particularly resistant and, when found by itself, is of little significance as
an indicator of recent pollution. But the organisms Nos. 2, 6 and 9 and the Oxytocus
perniciosus fall in with neither Savage's nor Houston's definition of " coli, " yet there is
some reason to believe that these bacilli are much more specifically an indication of
recent pollution than true B. coll. communis of Escherich itself.
A second example illustrating this important point will be found by referring to
the analysis of Cocanada water, page 117. The water at Cocanada is originally taken
from an irrigation canal ; it is run into a storage tank where it remains for anything
from seven days to a month ; it is then filtered and pumped into the town. The
canal sample contains fœ cal bacilli in 1 cc. ; but having been exposed to the sun for a
considerable time, as the water flows slowly for many miles down a shallow irrigation
canal, it has been so thoroughly well sunned and settled, that the only organism
present is B. grunthal. After the water has remained in the storage tank, this
organism has further decreased in number, till they are only present in 10 cc. of the
water. Now these two samples would he condemned as containing coli. The water then
passes through filter beds. As a result of this would-be filtration, the f œ cal bacilli
have run up from 1 in 10 cc. to 1 in ·3 of a cc. None of these samples alter filtration
contain any organism which, can be called. "true coli." It has been shown by inspec-
tion that the reason for this increase is due to the fact, that, more or less polluted
subsoil water finds its way through the masonry floor of the filter beds. Therefore
there can be no doubt that this admixture is distinctly undesirable, though the bacilli
added happen to be mainly B. cloac æ— an organism which neither Houston nor Savage
include within their definition " true coli, " and which (because it liquefies gelatine)
would be regarded as of no serious importance as an indicator of fœ cal contamination.