56
the emulsion a fine flocculent mass, that held the organisms entangled in its meslies;
this substance protected the bacilli from the action of the sunlight and gave most
erratic results. The unfiltered emulsions of human fœces took about 12 or 13 days
to become sterile, whereas the emulsion of cowdung took much less time. It was
decided that this mucous material must be removed by passing the mixture through
a cotton wool filter. Experiments Nos. 13, 14 and 15 give the results obtained from
these filtered emulsions. It will be observed how very different these are from those
of the unfiltered emulsion, and how rapid is the disappearance of organisms when left
entirely unprotected in the sun's rays. A filtered emulsion of cowdung gave results
almost identical with these ; so that it is obviously incorrect to suppose that bacilli
from the human intestine are more resistant to the action of sunlight than those that
inhabit the alimentary tract of cows ; the results of the previous experiment being
explained by the greater quantity of mucus in human fœces.
We now pass to the investigation of the action of sunlight on different varieties of
organisms met with in the f œces of human beings and. animals.
In the following series of experiments the technique was not altered and the same
quantities were used. In the case of the cowdung the emulsion was not filtered,
except in the cases (to be described later) when a layer of sand was placed at the bottom
of the dish.
Before describing the results obtained by the new set of experiments, we wish to
refer back to table VIII (a) giving results of experiment No. 1. Unfortunately we have
never succeeded in getting such an instructive sample of human fœces or cowdung as
this one proved to be, the results are very striking; it will be noted that the sample
originally contained. bacillus coli communis in such numbers as to preponderate over
the others in the original analysis. The emulsion was placed. in the sun about noon
of the 2nd September and by the end of the 3rd, that is to say, presumably after about
18 hours' exposure to sunlight, all the coli communis had. disappeared, and were never
found in the emulsion again. These coli being killed. off, an entirely new set of
organisms appeared in the analysis, namely, coscoroba, neapolitanus, pneumoniæ and
Nos. 100 and 101. By the evening of the 5th a further change had come over the
organisms in the emulsion, bacillus lactis ærogenes largely preponderated, acidi lactici,
grunthal and. cloacæ began to appear, and another organism No. 67 was present -for
the first time.
.A sample taken on the evening of the 7th shows still further alterations. A new
organism, namely, No. 33, which, it should. be noticed, belongs to MacConkey's group
No. 2, and. possesses reactions almost identical with those of coli communis itself,
appeared for the first time. Unfortunately for three days, only the dail y investi-
gation as to the presence of organisms in 5 cc. was taken ; on two more occasions
the operation of putting the organisms through the sugars was carried out. But these
results show that organism No. 101 preponderated and outlived most of those above-
mentioned. These results, incomplete as they are, give a fair idea of the order in which
the organisms died off under the action of the sunlight. The important point to
notice is, that in a fœces crowded with coli communis, these organisms had entirely
disappeared in less than eighteen hours, so that the various other more resistant
types were easily isolated.
Our main difficulty has been, at this time of year, to obtain samples of fœces that
contained. a good mixture of varieties. The cowdung was especially troublesome
in this respect.
E x p e r i m e n t N o . 1 6 — C o w d u n g .
Emulsion on exposure contained ...
4 coscoroba, 6 grunthal.
After 1 hour's exposure showed ...
9 grunthal, 1 cloacæ.
Do. 2 hours'
do.
..
10 grunthal.
Do 4 hours'
do.
.••
10
do.
Further sample taken at noon second day proved that the emulsion contained no.
more organisms in 20 cc.
Note.—This experiment is not very satisfactory on account of the small number of varieties.
originally present ; bacillus grunthal survived to the end.