A learned physician also thus wrote to the author of this chapter:
"The subject of the ventilation of our dwelling-houses is one of the
most important questions of our times. How many thousands are victims
to a slow suicide and murder, the chief instrument of which is want
of ventilation! How few are aware of the fact that every person, every
day, vitiates thirty-three hogsheads of the air, and that each
inspiration takes one fifth of the oxygen, and returns as much carbonic
acid, from every pair of lungs in a room! How few understand that after
air has received ten per cent of this fatal gas, if drawn into the
lungs, it can no longer take carbonic acid from the capillaries! No
wonder there is so much impaired nervous and muscular energy, so much
scrofula, tubercles, catarrhs, dyspepsia, and typhoid diseases. I hope
you can do much to remedy the poisonous air of thousands and thousands
of stove-heated rooms."

In a cold climate and wintry weather, the grand impediment to
ventilating rooms by opening doors or windows is the dangerous currents
thus produced, which are so injurious to the delicate ones that for
their sake it can not be done. Then, also, as a matter of economy, the
poor can not afford to practice a method which carries off the heat
generated by their stinted store of fuel. Even in a warm season and
climate, there are frequent periods when the air without is damp and
chilly, and yet at nearly the same temperature as that in the house.
At such times, the opening of windows often has little effect in
emptying a room of vitiated air. The ventilating-flues, such as are
used in mines, have, in such cases, but little influence; for it is
only when outside air is colder that a current can be produced within
by this method.