446 THE TROPICAL 
minute cells, having a very brief inclividual exis- 
tence. They are divided into groups, such as moulds, 
alg», fungi, yeasts and bacteria, and it is principally 
those of the latter class with which we h ive to deal. 
An important point in the lite history of Bacteria 
is that, whilst some! of them thrive in the pres ^noe 
of a plentiful supply of atmospheric oxygen, others 
have a more healthy existence in its absence. The 
former are called serobic bacteria, the lalter an;ero- 
bic bacteria. Another point is that they all live 
on food of complex character. Whilst the higher 
plants feed on very simple foods, such as ca-bonic 
acid and nitrates, building up from these the com 
plex compounds, carbo-hydrates, oils and albumens, 
these lowly orgai isms perform the reverse opera- 
tion, and, feeding on complex material, break it 
down, with the production of simple substances, 
some of them proceeding so far aa the production 
of carbonic acid and nitrates. Furthermore, whilst 
one organism will prefer the most complex material 
as food, producing therefrom simpler substances, 
others have a particular appetite for these simpler 
substances and reduce them to compounds of a still 
more simple constitution. 
It is indeed, as has been mentioned in a former 
part of this lecture, owing to the existence of my- 
riads of such organisms, that the vegetable and 
animal matter, which accidentally or by the agency 
of man are annually deposited in the surface soil 
of our fields, rapidly disappear and become changed 
into the simpler compounds on which the higher 
plants feed. 
The action of these bacteria has very pertinately 
been likened to that of a child, who after assisting 
in building up a castle from a pack of cards, pro- 
ceeds to take a card first from one part of the 
structure, then from another, \\ith the result that 
the castle is rapidly converted into a heap of cards 
again. 
Finally, I must refer o another characteristic of 
these organisms, and that is, they don't like their 
food to be too concenirated. If they have too much, 
they suffer in the same way, as a boy does who 
eats too many sweatmeats at once. They get ill and 
may die, if the excessive food supply is persisted 
in. This really explains why the sewage farm has 
been a nuisance instead of a blessing. Vast qaan- 
tities of mitertal have always been poured upon a 
small area, without any consideration for the health 
of our microscopical friends, and the result has been 
that they couldn't perform their duty satisfactorily, 
and the sewage farm proved a failure. 
We may now return the biological treatment of 
sewage, with a clearer understanding of the condi- 
tions involved in its arrangement. For it to pro- 
ceed satisfactorily, we must offer the material to 
these organisms in such a manner that each class 
may perform its appointed task — the anserobic or- 
ganism prefers to be without air, the aerobic microbe 
must have an abundance ; the food must also be 
in a reasonably diluted state ; and thirdly, ne must 
not upset the home or colonies which these classes 
make for themselves, for they sort themselves out, 
and one class will inhabit one spot in the biological 
filter, another class another, and if we give crude 
sewage to the class which lives on the partly 
simplified material, the result will be destruction, 
not to the sewage but to the microbe. 
Thus in the case of the filter which Dibdin, 
^ott-Moncrief , Garfield and others have used, the 
ciude sewage passes first into one vessel, which 
Mr. Scott-Moncrief has called a " cultivation tank." 
This is simply a large tank filled with broken brick 
or some o'.her coarse material. Here those organisms 
which prefer the more complex organic foods thrive 
particularly, dissolve it and reduce both this, as 
likewise the other soluble matters, to simpler sub- 
stances. In this tank little or no air is admitted. 
The I'csulting c llluent then passes to a series of so- 
callfcd " fillort)," to which I will return presently. 
j, Jeave the "cultivation tank" t9 ^eserilje very 
AaRICULTURlST. [Jan. 1, 1902. 
briefly what is called the "septic tank." The 
author of this is Mr. Cameron, the City Surveyor 
of Exeter, who also took up the biological treatment 
of sewage a few years ago. His experiments took 
a slightly different line. Whilst Dibdin and others 
passed the sewage into a tank filled with broken 
brick or coke, Came/on tried the effect of allowing 
the sewage to remain in a simple closed tank (con- 
taining no broken material) for some hours, Jind 
found as a result that the sewage was rapidly purified 
in a great measure. A tank was then erected of 
such dimensions, that the sewage of a portion of 
the town might constantly flow into it at one end 
and pass out at the other, the time occupied being 
about 2i houfs. It was then found that in fact 
great changes took place in the sewage. By means 
of a "manhole'" from which the interior of the tank 
could be observed, it was seen that the solid matter 
would first settle to the bottom, then rise with 
bubbles of gis to the surface, then fall again, and 
apparently this process goes on from one end of the 
tank to the other, A scum, consisting of organic 
matters, forms on the surface, which seems to ba 
thicker in winter than in summer, but never re- 
quires removal, and an ash-like deposit collects very 
slowly on the bid of the tank, which consists largely 
of mineral matters. G- ises are evolved in this tank 
consisting lari<ely of mathane, with some carbon di- 
oxide, and this is utilised to illuminate the work? 
at night. The tffl lent from this septic turik is free 
from smell and is clear. Like the efllient from 
DibJini's bacteria tank, it then passes to the bio- 
logical filters. 
These consists of simple vessels filled v.-ith broken 
material, such as coke, and here the efliuent ia 
allowed to remain for several h jurs, after which it 
pisses out, and the fil'eris left empty for purposes 
of aeration before being filled ag^in. 
By an ingenious device, due to Mr. Cameron, the 
flow of water from the septic tank, opens the tap 
of one, or closes that of another filter at the proper 
time, thus enabling the series to woi k automatic:illy. 
The raw sewage runs directly into the septic tank 
continuously, and passes from it again sim'ilarly ua- 
informly to the filters, wiiich, as I have said, work 
autom itically. The apparatus requires therefore a 
very small amount of supervision. 
The effluent from the filters is not on'y free from 
odour, it is so pure that it remains perfectly clear 
and bright for any lengih of time in closed bottles, 
which is one of the severest tests of the purity of 
water, and it has baen drunk by more than one 
person without any ill effects whatever. Thus 
putting the matter very briefly, one class of organisms 
inhabit the septic tank or "bacteria tank"'; these 
thrive on complex organic food, and are largely 
anaerobic in character. Then, secjndly, the bio- 
logical filters are inhabited by another class of 
organism, which are aerobic and feed on the more 
or less simplified materiil, converting it into still 
simpler matters. The chemical changes may be very 
briefly described as follows : the carbo-hydrates are 
reduced to cirtaon di-oxide aL->d mathane, the albumi- 
noids and amides first to ammonia and then largely 
to nitric acid. 
And now you will doubtlessly agree with me that 
the value of tiie biological treatment of sewage is 
just as importarjt to' agriculture as it is to the 
sanitary authorities. Especially is this so here in 
India. Not satisfied with converting the farm 
manure into fuel, the attempts to utilise the city 
manure have been generally of just as ruinous a 
description. A dry-earth system, which if it conld 
be perfectly carried out, could not readily be im- 
proved upon, has been converted into a general 
nuisance ; the whole of the manure has been placed 
in a few square yards of land, to the utter ruin of 
our friend the microbe. Wuggestions that the 
manure should be given in smaller doses over a 
large area have been met by the rejoinder that 
auch wa9 impraotioable, Now, likewise in the <)m% 
