mal matter, and, however dry the
atmospheric air may be, the expired air is always saturated with watery
vapor, and, no matter what the temperature of the external air may be,
that of the exhaled air is always nearly as warm as the blood. An adult
man on a average breathes about sixteen times in a minute and at every
inspiration takes in about thirty cubic inches of air, and at every
expiration exhales about the same amount. Hence, it follows that about
16-2/3 cubic feet of air are passed through the lungs of an adult man
every hour, and deprived of oxygen and charged with carbonic acid to the
amount of nearly five per cent. The more nearly the composition of the
external air approaches that of the expired air, the slower will be the
diffusion of carbonic acid outwards and of oxygen inwards, and the more
charged with carbonic acid and deficient in oxygen will the blood in the
lungs become. Asphyxia takes place whenever the proportion of carbonic
acid in the external air reaches ten per cent., providing the oxygen is
diminished in like proportion, and it does not matter whether this
condition of the external air is produced by shutting out fresh air from
a room or by increasing the number of persons who are consuming the same
air; or by permitting the air to be deprived of oxygen by combustion by
a fire. A deficiency of oxygen and an accumulation of carbonic acid in
the atmosphere, produce injurious effects, however, long before the
asphyxiating point is attained. Headache, drowsiness, and uneasiness
occur when less than one per cent. of the oxygen of the atmosphere is
replaced by other matters, and the constant breathing of such an
atmosphere lowers vitality and predisposes to disease.

Therefore, every human being should be supplied, by proper ventilation,
with a sufficient supply of fresh air. Every adult individual ought to
have at least 800 cubic feet of air-space to himself, and this space
ought to communicate freely with the external atmosphere by means of
direct or indirect channels. Hence, a sleeping-room for one adult person
should not be less than nine by ten feet in breadth and length and nine
feet in height. What occurred in the Black Hole at Calcutta is an
excellent illustration of the effect of vitiated air. One hundred and
forty-six Englishmen were confined in a room eighteen feet square, with
two small windows on one side to admit air. Ten hours after their
imprisonment, only twenty-three were alive.

V