storeys, the health of those who work on the upper floors always
suffers most.

In the old monkey-house of the Zoological Gardens, when the cages
were on the old plan, tier upon tier, the poor little fellows in
the uppermost tier--so I have been told--always died first of the
monkey's constitutional complaint, consumption, simply from
breathing the warm breath of their friends below. But since the
cages have been altered, and made to range side by side from top
to bottom, consumption--I understand--has vastly diminished among
them.

The first question in ventilation, therefore, is to get this
carbonic acid safe out of the room, while it is warm and light and
close to the ceiling; for if you do not, this happens: The
carbonic acid gas cools and becomes heavier; for carbonic acid, at
the same temperature as common air, is so much heavier than common
air, that you may actually--if you are handy enough--turn it from
one vessel to another, and pour out for your enemy a glass of
invisible poison. So down to the floor this heavy carbonic acid
comes, and lies along it, just as it lies often in the bottom of
old wells, or old brewers' vats, as a stratum of poison, killing
occasionally the men who descend into it. Hence, as foolish a
practice as I know is that of sleeping on the floor; for towards
the small hours, when the room gets cold, the sleeper on the floor
is breathing carbonic acid.

And here one word to those ladies who interest themselves with the
poor. The poor are too apt in times of distress to pawn their
bedsteads and keep their beds. Never, if you have influence, let