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14
upon from the great chalk formation. In proportion as the number of these wells has
increased, and the quantity of water drawn has been greater, the level of the water
has gradually fallen.
4th.—The Water Companies. The quality of the water supplied by both the
New River and East London Companies is so indifferent that it would scarcely answer
any useful purpose to contrast them with a view to showing which is the best—both
waters are essentially impure; they contain a large, and no doubt injurious amount of
organic matter; they are both hard.
the air.
The air of a populous district derives its impurities from two principal sources:
first, from the emanations rising from the soil; secondly, from the exhalations given
off by the processes of animal respiration and transpiration. To these may be added
a third source of contamination mostly of local action, but often of serious import:—
the gases and effluvia arising from manufactories of various descriptions.
In a certain degree of concentration, the poisonous properties imparted to the
air from any one of these sources may be injurious to health, and even destructive of
life. The virulence of the aerial poisons of the two first classes, when highly concentrated,
has often been fatally exemplified. Men who have incautiously descended into
sewers have been instantly killed: poisons which act thus powerfully in a concentrated
state may be expected to act injuriously, although less obviously, when more diluted:
that is, diffused through a larger body of air. If dilution be carried further still, so
that the aerial poison shall be reduced to a very infinitesimal proportion of the air, it
may be rendered, if not absolutely harmless, at any rate, very nearly so. These considerations
point to one great agent in sanitary medicine, namely, the supply of
abundance of fresh air, and its free circulation through every spot, and every house
and room exposed to the evolution of aerial poisons. It unfortunately happens that
many of those localities, where the developement of gaseous poisons is most active,
present the most unfavourable conditions for ventilation. Fresh deleterious matter is
being constantly poured into the air, whilst no adequate circulation exists to carry it
off, or to dilute it. I have, for instance, become acquainted with several cases of the
following kind:—in a row of houses there will be one situated on a lower level than
the rest, and frequently at the same time more shut in and deprived of light and air.
If the sewerage and drainage of this row be defective, the overflowing and oozings
from the cesspools of the whole will gravitate towards the doomed house at the lowest
level; the ground will be kept saturated with decomposing matter, always emitting