Medical Officers of the Army of India.
found far more generally useful and less expensive; at the same time, it may be advisable
in certain places (and each case must be considered on its merits) to use the closed septic
tank. But one word of caution: we must not fail to give the first stage (of hydrolysis) fair
scope, whether we use the closed septic tank as the upward filter bed. There are temp
-tations to reduce the size of these, and the thickness of the filtering medium in the latter,
with the avowed object of what is called "macerating" (in the sense of breaking up
the solids into a sort of purée), which must be resisted, if we are to escape disaster, by
minimising the process of hydrolysis (fermentation) and so confusing the subsequent
processes, for which due preparation in the first stage is essential. An eminent Sanitary
Engineer from England recently gave a specification for an upward filtration bed, allowing
only one cubic yard of filtering material for the excreta of nearly 200 natives ("1,000
gallons," composed of the excreta of each person diluted with 5 gallons of water). This,
I am convinced, will never do, and was based on the idea that the sewage of the town in
question was of a similar strength to that of London, whereas it was 12 to 15 times
stronger. Nothing is so dangerous as a rule-of-thumb method in matters involving vital
processes.
Lastly, should it be desired to make a comparative trial on a small scale of
both forms of apparatus, the writer will be glad to exhibit a rough sketch
plan of a simple device by which different strengths of sewage can be treated, by
which the flow into the septic tank can be graduated and the level of the fluid
in the tank kept constant—all most important factors in the success of the
biological processes.
The simple form of installation advised and figured (Plate I, figures 1, 2 , 3)
is to be taken as a type, and not a hard-and-fast design guaranteed to meet all
conditions. It has always to be borne in mind that we are dealing with vital
forces that must be studied to be effectually controlled; the play's the thing and
not the stage, and the latter must be adapted to the former. This specification
is not drawn up to meet the theoretical minimum requirement, but is based on
practical experience of an effectual working apparatus. The cost has been esti
-mated by a practical Engineer, on military works rates, to run to about £ 150, but
this will vary according to the filter capacity required, which will vary with the
total daily volume of sewage; this sum does not include the cost of the filtering
material.
3. Water-supply.—A few words as to the water-supply. Given an unpol
-luted soil, there is probably no safer nor more economical source than the spring
-level water tapped by means of properly protected wells. There is abundant evi-
dence of the dangers to which gravitation supplies from rivers, tanks and surface
springs are open, and no filtration process of a polluted supply can be held to
justify its use save under exceptional circumstances, of which the most valid is
that there is no choice.* Wells must be chosen or made, with due regard to
* See remarks by the Bacteriologist, North. Western Provinces and Oudh, as to the relative purity of filtered river
-water and the supply from wells at Agra.—Report of Sanitary Commissioner (India) for 1899, P. 49.
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