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48
It will be observed that a large number of old drains
still continue to bo discovered and abolished, as also
old cesspools. They are both great sources of atmospheric
pollution and danger to health; they are the
factors whence specific infection may actually originate,
or if not they have often palpably retained it
locked up for years, and until discovered, causing mysterious
visitations of typhoid or scarlet fever.
The modern main drainage system in the Metropolis
has proved that it is comparatively easy to get rid of
the solid and liquid sewage from our houses and doors,
but that it is not so controlable when it assumes a
gaseous form in the great sewers, where it will not, of
course, circulate with the liquid and suspended sewage
and escape with it from the mouths of the sewers, but
rises or is forced just sufficiently high both in houses
and out of doors to become unavoidably respirable.
Viewed in this light, the great modern sewerage system
of the Metropolis is a greater source of atmospheric
pollution than was the old cesspool system with all its
local objections and abominations, and to which of
course wo could not return. The vexed questions to bo
solved arc effective sewer ventilation and prevention of
sower deposits, whence the most noxious and offensive
effluvia arise, and efficient and general smoke consumption,
both domestic and manufacting. Hence the chief
sources of general atmospheric pollution in the Metropolis,
are smoke, sewer gases, and suspended matter
arising from all kinds of sources, organic and inorganic,
from the products of respiration of living beings, and
from the comminuted filth of the streets. This condition
of the London air is often palpable enough,
especially when its pressure is great and movement
slow, so that those impurities cannot escape producing
effects, of which general lassitude and mental depression
are often the least injurious. We should be at least as