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been considered, and some further natural laws governing the 
health of households, especially in isolated habitations, having 
been set forth, there remain for treatment only the laws which 
operate in the special set of conditions produced by that close 
contiguity of dwellings characteristic of cities and towns. 
The total amount of fluid and solid impurities of all kinds cast 
forth from the kitchens and other parts of more than a given 
number of houses per acre of ground—irrespective of dust-bin 
refuse which can be removed by cartage—-quite overtasks the 
natural chemical purifying powers of that ground. Hence, in the 
first place, pure water cannot be obtained from wells sunk in such 
ground, and must therefore be brought to the town from some 
distant area by a system of open and closed mains and pipes. In 
the second place, especially with a somewhat larger number of 
houses, the total quantity of impurity cast forth becomes such a 
source of contamination, not only to the water of wells in the 
neighbourhood, but to the air, that it must be taken away from the 
town by a system of pipes, drains, etc., to some distant area. Here 
the laws of nature cannot be evaded; and their working is simple. 
A household must, in nearly every case, get its supply of water, 
say twenty or thirty gallons per head daily, from the earth, and 
when that water has done its duty of washing, cooking, etc., it 
must be returned to the earth. If the dwelling is isolated in an 
acre or so of porous ground, this intake of pure water and output of 
sullied water may go on within that area. If dwellings are crowded 
together, the intake of pure water must be from a distant area in one 
direction, and the output of sullied water must be to a distant area in 
another direction. But in both cases there must be ground whence 
to draw the clean water and ground on which to cast the dirty 
water. In both cases too we may trust to nature, and we may 
implicitly trust her, to convert the impure water into pure water 
ready again for the use of man. Bor, be it remembered, the stock 
of water in the world never varies. The water man has used 
before he will use again, and again, and again; each time perfectly 
purified in nature’s perfectly appointed laboratory. It may be 
that a given country, in its wisdom, believing that it is choosing 
the lesser of two evils, elects to send more or less of its sullied 
water direct to its rivers and so into the sea. In that case the 
only variation in effects—in the intermediate effects—will be that 
the country will pro tanto lose the manurial value of that sullied 
water. Further, to the extent to which a country thus incurs an 
expenditure larger than its income, will it sooner or later become 
bankrupt. The result may not ensue for many generations, but 
