53
that (i) the organisms present in cowdung were more rapidly killed by the action
of the sun than were those derived from human fces (this was found on further
experiment not to be the case), (ii) that eoli communis does not survive exposure
to the sun for very long, (iii) in the majority of the samples bacillus grunthal was the
last to disappear.
The next series of experiments was carried out with much greater care. It was
thought that the absence of organisms from 5 cc. of the emulsion of cowdung or human
fwces was scarcely sufficient to prove that the organisms had entirely disappeared.
Consequently in the next series of experiments 20 cc. of the mixture were used. As
previously the emulsion was not filtered, but the solid particles coming from the
fœeal matter were exposed with the clearer water. Before taking the samples, the
mixture was thoroughly well stirred up, the gross sediment was allowed to settle,
and the sample taken with a sterile pipette from the clear fluid. In this series of
experiments 4 grams of cowdung or human fces were weighed out, and added to 3
litres of water. An attempt was made to keep the depth of fluid in the dish constant.
That is to say, the dishes being about 2 1/2" deep, they were filled up to the same point
on all occasions. Some emulsions were somewhat yellow in colour, and it seems.
highly probable that this colouration of the mixture had something to do with the
rapidity or otherwise of the action of the sun.
Experiment No. 6.—Three dishes of contaminated water—one containing human
faeces, one containing eowdung-and one of Adyar water, were exposed to the sun
simultaneously. ( The Adyar water is taken from the river Adyar, which runs close to
the King Institute ; it is very highly polluted by the washing of clothes ; an analysis
of this water show that it contain coli communes, lactis æærogenes, and acid lactici).
From each of these dishes 20 cc. of the mixture was taken and put in bile salt lactose
broth. This was the only reaction taken. The formation of acid and gas in the
medium showing that fcal bacilli were still present in 20 cc. of the emulsion. The
samples were taken about 5 in the evening every day. The result showed that
bacilli were present in 20 cc. for 7 days in human fces, for 7 days in the emulsion of
cowdung, for 3 days in the Adyar water. It should be noticed that this experiment
was commenced on the 1st of December, when the sun was very near its lowest point.
Experiment No. 7. —Was carried out on exactly the same lines as the above.
The emulsion of human faces contained faecal bacilli in 20 cc. for 13 da
fÒcal
ys'
continuous exposure to sunlight. The emulsion of cowdung contained none of
these organisms in 20 cc. after the sixth day. The Adyar water was also free from
these organisms on the sixth day ; the samples taken on the third and fourth day
'showed no bacilli in 20 cc. though the one taken on the fifth gave the reaction. Four
subsequent samples showed that the bacilli had actually disappeared.
Experiment No. 8.—A dish of emulsion of human faeces and one of Adyar water
were exposed to the action of the sun. The emulsion of human fces continued to
show faecal bacilli in 20 cc. of the mixture for 13 days, Adyar water showed them in
20 cc. for only 3.
It is not maintained that these experiments in themselves demonstrate more
than the fact, that, even a very highly polluted water will, in time, be rendered
practically sterile by the action of the sun. In these experiments it is admitted,
that the sun had probably a more rapid sterilizing action than occurs under truly
natural conditions, but it is obvious that, given time, organisms will entirely
disappear due to the action of the rays of the sun.