23
organisms had disappeared. Consequently, in order to ascertain the period during
which coli communis will remain living in the ground, investigations on trenching '
grounds probably do not constitute the most satisfactory method.
A comparison should be made between the results of all the older samples of
trenching ground earth and. those of the Ootacamund sewage farm earth ; a striking
difference will be apparent at once. The longer the night-soil remains in the ground
the smaller the number of varieties of organisms are . isolated. Thus the freshly
contaminated earth in the sewage farm contains no less than nine varieties of lactose
fermenters . The oldest samples seldom contain more than one, or at the most two,
varieties. It would, we consider, be reasonable to conclude that these organisms have
outlived the other varieties, and are better able to resist the various forces that are
.active in soil.
Now referring to the organisms which have been -found to persist, it will be
observed that bacillus . cloaca is the commonest of these. Bacillus grunthal and
bacillus coscoroba and bacillus No. 73 appear to be very resistant organisms and are
capable of maintaining their existence, under favourable conditions, for very consi-
derable length of time, probably up to 3 or 4 years or even longer. These facts are
very important in themselves, and if the investigation of these polluted earths had
revealed nothing else it still would have been worth undertaking,
On the other hand, whilst not laying too much importance on the negative result
obtained in the course of this work, it is very striking that in no case has coli communis
been isolated. There can, however, be no doubt that the entire absence of this
organism from these analyses, supports the opinion, arrived at by Houston and other
workers, that bacillus coli communis (Houston's " coli " was probably very largely
made up of coli communis), does not remain alive for any very considerable length of
time, when introduced into the soil.
The obvious objection to drawing conclusions from so artificial an arrangement as
that of a trenching ground have already been referred to viz., the enormous volume of
night-soil put into a trench ; this could scarcely be said to be on a parallel with the
usual method by which fecal contamination would penetrate into the ground. In
order to obviate these objections two experiments were started up within the compound
of the King Institute-
1. A trench was dug in the ground 9 inches deep and a foot wide and about
6 or 8 feet long. A small quantity of night-soil, just sufficient to cover the bottom of
this trench, was mixed with dry earth placed- in the trench and covered up. This
arrangement gives every possible chance for the ground to absorb the moisture in the
night-soil, and to bring to bear any influence that earth may possess in destroying organ-
isms, further it resembles in a measure what actually goes on in nature. Samples
of this contaminated earth have been analysed from time to time and the results are
given in abbreviated form below :—
The trench was prepared. on 23rd December 1908.
Sample (1). Shortly after the trench was prepared there was some very heavy
rain. The water was actually standing over the trench when this sample was taken,
that is on 4th January 1909. One gram of earth was used for each analysis. Out of
13 colonies examined all were bacillus grunthal.
Sample (2) taken on 11th January 1909 showed the following analysis : 5
coscoroba, 1 acidi lactici, cloacae, 2 grunthal.
Sample (3) taken on 20th January 1909 showed the following analysis : 1 coli
communis, 3 coscoroba, 1 neapolitanus, 1 cloaca, 3 bacillus No. 75.
Sample (4) taken on 27th January1909 showed the following analysis : 2 coli
Communis, 3 grunthal, 3 neapolitanus, 1 cloacm, 1 coscoroba.
Sample (5) taken on 8th February 1909 showed the following analysis : 1
Coli communis, 4 grunthal, 3 coscoroba, 2 neapolitanus.
Practically no rain has fallen since that recorded when sample (1) was taken
on 4th Jannary 1909.
Sample (6) taken on 15th March 1909 showed the following analysis : 2
grunthal, 2 coscoroba, 2 neapolitanus, 1 cloaca, and 3 rare organisms No. 33.
Sample (7) taken on 23rd March 1909 showed the folowing analysis : 2
grunthal 6 coseoroba, 2 neapolitanus.