Take another instance, which is only too common: If you are in a
crowded room, with plenty of fire and lights and company, doors
and windows all shut tight, how often you feel faint--so faint
that you may require smelling-salts or some other stimulant. The
cause of your faintness is just the same as that of the mouse's
fainting in the box; you and your friends, and, as I shall show
you presently, the fire and the candles likewise, having been all
breathing each other's breaths, over and over again, till the air
has become unfit to support life. You are doing your best to
enact over again the Highland tragedy, of which Sir James Simpson
tells in his lectures to the working-classes of Edinburgh, when at
a Christmas meeting thirty-six persons danced all night in a small
room with a low ceiling, keeping the doors and windows shut. The
atmosphere of the room was noxious beyond description; and the
effect was, that seven of the party were soon after seized with
typhus fever, of which two died. You are inflicting on yourselves
the torments of the poor dog, who is kept at the Grotto del Cane,
near Naples, to be stupefied, for the amusement of visitors, by
the carbonic acid gas of the Grotto, and brought to life again by
being dragged into the fresh air; nay, you are inflicting upon
yourselves the torments of the famous Black Hole of Calcutta:
and, if there was no chimney in the room, by which some fresh air
could enter, the candles would soon burn blue, as they do, you
know, when ghosts appear; your brains become disturbed; and you
yourselves ran the risk of becoming ghosts, and the candles of
actually going out.

Of this last fact there is no doubt; for if, instead of putting a
mouse into the box, you will put a lighted candle, and breathe
into the tube as before, however gently, you will in a short time