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CHAPTER VII,
A STUDY OF THE BACTERIOLOGY OF THE FACES OF MAN AND OTHER
ANIMALS,
Of all the pollutions that water is liable to, that due to the faecal discharges of
man and animals is by far the most important ; hence, if a correct interpretation is to
be put on the results of the bacteriological analysis of water, it is absolutely essential to
study the micro-organisms present in dejecta generally. Early in the course of this
work we commenced. a study of the bacteriological flora of faeces, choosing particularly
the fces of man and cattle, In towns in India, the pollution of water is
largely human in origin, whereas in areas of sparse population faecal organisms are in
the main derived from animals, Our object in making these analyses was primarily
to see (i) what organisms we might expect to get in water ; (ii) whether the results of
analyses of faeces, obtained at Home, by MacConkey ( 1905) and others, were similar to
those in this country ; (iii) whether any particular organism exists in human faeces
and not in cowdung or vice versa and (iv) whether the relative percentage of the
various organisms (or the percentage in MacConkey's four groups) in human and animal
faeces could be worked out, so as to demonstrate the existence of any constant relation
between the bacteriological flora in each, The work of MacConkey (Journal of
Hygiene, 1905 and July 1906) shows that the relative percentages in the four groups
differ in the dejecta of man and cows,
Nine different series of analyses were made at various times of the year begin-
ning with July 1908 and ending with March 1909. The time of the year when these
experiments were made was found to be important,
Concerning the method used in the course of this work, it may be remarked, that,
whenever it is not stated to the contrary, the following is the procedure adopted ;
a loopful of faeces was put in the MacConkey's broth, incubated for 24 hours,
the resulting growths were plated out on bile salt lactose agar, and the colonies
obtained were put through the sugars exactly in the same way as the organisms isolated
from water. In some of the series, however, a small particle of faces was plated out
straight on to the solid medium, without passing through bile salt broth.
Series No. 1 consists of 150 colonies taken in the months of July and August
from 11 different samples of cowdung and human fces,
Series No. 2 was made at the end of August and consists of two sets of 150
colonies each derived from nine different samples of cowdung and human faeces
respectively,
Series Nos. 3 and 4 are different from others. In the case of series No, 3 it
was thought, that, instead of using separate samples, a mixture of faeces from 10
individuals, or 10 calves, would give a greater variety of organisms ; and that the
classification of 50 colonies taken from a mixture would be of greater value in work-
ing out the percentage of prevalent organisms, than by taking the total of the colonies
from the ten separate samples. Series No. 3 was put in bile salt broth in the ordinary
way. The result shows at a glance how entirely these experiments failed in the object
for which they were designed, there being only four separate species isolated in each
case [-vide table VII (c) j.
Series No, 4 was made on exactly the same lines, a mixture of faeces being used,
but it was thought that better results might be obtained by plating small portion of
the mixture direct on to the solid medium. In this series 30 colonies from a mixture
of human faeces and 30 colonies from a mixture of cowdung were examined. It will
be observed that no very great difference is shown between the results obtained
in the two series. This experiment also incidentally demonstrates that bile salt broth
has little or no influence in altering the numerical relation of the micro-organisms.