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JOURNAL OF THE PLYMOUTH INSTITUTION. 
probability till the village is sufficiently developed to warrant a 
proper system of drainage. 
Drains are porous channels to carry off the surplus land water, 
while sewers are, or ought to be, perfectly impervious channels for 
the conveyance of sewage. To make drains act as sewers is, as we 
have seen, highly dangerous where the drains, instead of giving 
off surplus water, absorb liquid sewage during drought. 
Much has been written on the advantages of a double system of 
channels — one pervious, the other impervious. In towns the only 
objection, and that will not long be one, is the great cost of a 
double system of channels. Those who are conversant with drain- 
age will remember that along the outside of all sewers, however 
carefully filled up, there is a great weeping or draining of land 
water, nature carrying out the separate system on her own account. 
We have already seen how evils from negligence in sanitary 
matters press themselves home on us through the water we drink, 
the air we breathe, and the contacts we make ; and we will now 
proceed to consider the disposal and treatment of sewage as most 
applicable to our case. 
The dry earth system has now been in successful use for many 
years at a large number of small towns and villages, and with the 
best of results where the scavenging arrangements are good. The 
cost of working this system in a village of about 500 inhabitants 
is almost balanced by the sale of the manure, which is worth about 
£1 per ton. Local authority is a first necessity in all cases of 
sanitary reform, notably so in the dry earth system, where, in 
addition to the initiation of the scheme, there is the constant detail 
of working. 
It is hard to see how so rudimentary an operation as sewage 
farming cannot be attempted on a small scale. Yet this is the 
opinion of many in power. 
Land, in the first place, must not be surcharged with sewage ; if 
so, the root crops rot, and the grass too, after the first crop goes oil". 
Sewage farming, carried on purely for its agricultural value, is the 
only permanently healthy condition of sewage utilization. In this 
country few farm crops require the application of sewage oftener 
than six times per season, many not so often. Garden produce, 
such as cabbage, absorbs more than three times this quantity, and 
such cultivation is thus very suitable for sewage farming. 
A process fortunately goes on known now as intermittent down- 
