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CHAPTER IV.
STUDY OF BACTERIOLOGY OF EARTH KNOWN TO BE HEAVILY POLLUTED.
.
The study of the effect of gross animal pollution on the soil, and the way in which
mature gets rid of the effects of this pollution, is a subject which is very intimately
bound up with that of the bacteriology of water, particularly in rural areas of India,
where surface wells are the commonest source of drinking water. Houston and
other bacteriologists have shown that fœcal organisms when added to an ordinary
cultivated soil gradually disappear ; that is to say, there is a power in the soil to cleanse
itself from contamination. The forces which bring this about are many, and the
complete understanding of these phenomena cannot be expected from the analysis of a
few samples of earth. But, as the results obtained from a study of one phase of this
question bear, to some extent, on the conclusions arrived at in the other chapters of
this report, we consider it desirable briefly to describe these.
In this country land in the neighbourhood of villages and towns is polluted with
human excrement to a degree which is almost incredible to any one who is not conver-
sant with oriental conditions. Latrines may be constructed, but it is certain that
practically the whole of the male, and some part of the female, population prefer to go
out into the neighbouring fields rather than to make use of such arrangements ; it is
only in large cities, where fields are at considerable distance from the houses, that
latrines are used to any extent ; even then a fair proportion of the inhabitants,
particularly children, simply make use of waste pieces of land and by-lanes right in
the midst of houses. The fœcal discharges deposited in this manner are not buried in
the manner customary among the Jews, but simply left to the drying action of the sun
and hot winds ; in many soils in India the fœcal matter is first covered up with earth by
ants and then removed into the soil. Naturally in rainy weather it is washed into the
soil, if the latter be of a sufficiently porous nature. It should also be stated that a
population living under these conditions almost invariably derives its water-supply
from either shallow wells or tanks (ponds), into which surface water can find its way.
As a preliminary to a study of this very complex subject we have examined some
samples of earth which we know to be highly contaminated. There exists in this
country a very simple way of obtaining such samples of earth, which we are perfectly
certain have been grossly contaminated, namely, by taking specimens from trenching
grounds. These possess a decided advantage over the casual sample obtained outside
a village, for it is possible to ascertain the exact time when contamination took place.
In nearly all the towns, with the exception of the Presidency cities, fœcal matter is
removed by carts and is disposed of by burying it in the soil at a depth from 9 to
18 inches. Some of these olde rtrenches can be opened, and samples of the earth
from them taken, to study the organisms of a fœcal origin that persist in this soil. It
will be obvious that there can be absolutely no doubt of the thorough nature of
the contamination of the earth. It is not our purpose here to discuss the pros and
cons of this method of disposal of night-soil, but it suffices to say that it is cheap,
and if carried out carefully, in properly selected plots, remote from wells, and in
suitable soil, is free from any very serious sanitary objection. In some cases the land
that has been so trenched is ploughed up and cultivated 12 months after the
trenches have been filled in, and in others the earth taken from these trenches is sold
as manure.
The analyses given in the following work are those of samples of earth taken at
various intervals after the night-soil has been deposited in the ground. The kind of
soil varies considerably from a heavy clay to what is practically sea sand : —
Sample (1).—For purposes of comparison, analyses of soil taken from the sewage
farm at Ootacamund is also given. A small plot of ground was chosen, irrigated
with septic tank effluent for six consecutive days, allowed to dry for two days, three