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sary for the healthy development of the animal as well as the vegetable
kingdom.
The consequences of want of light are more perceptible, and, therefore,
more familiar to us in the vegetable kingdom; and are remarkably shown
in the properties and chemical products of plants reared in the open day or
in the dark.
The tendency of plants in a room to turn themselves to the light, the peculiar
want of colour and succulent growth of plants grown in the dark, and
the advantage which gardeners take of this property to bleach celery,
endive, &c., will sufficiently illustrate this part of my subject.
But human beings are equally dependent upon light; without light they
become cachectic and unhealthy; blanched from loss of the red colour of
the blood; debilitated and dropsical; scrofula is developed, and they will
probably be carried off by tubercular disease, or rendered fit prey for
epidemics.
Mothers living in dark cellars produce an unusual proportion of defective
children.
In some cells under the fortifications of Lisle, a number of poor people
took up their abode. The proportion of defective infants produced became
so great, that it was found necessary to issue an order commanding that
these habitations should be closed up.
But even in cases where the absence of light is less complete, the effects
are abundantly striking in the pale and sickly complexion and stunted frame.
The diseases the want of it produces are of long continuance, and waste
the means of life before death results; and as to death itself, it has been
calculated that in London nearly 10,000 persons perish annually from deficient
circulation of air and want of light.
Cause II. Want of Ventilation and, Free Circulation of Air.
An adult respires about 17 to 20 times in a minute; and it is calculated
that during an ordinary inspiration about 25 cubic inches of atmospheric
air are taken in, and about the same quantity expelled during an
ordinary expiration.
The gas taken in is atmospheric air; that which is expelled differs
materially.
"We find, that the greater portion of oxygen (constituting about one-fifth
part of atmospheric air), has disappeared; and that it is replaced by an
equal volume of carbonic acid gas, an additional quantity of which is
eliminated by the skin.
Carbonic acid is a poisonous gas, 13 to 15 per cent, of which mixed with
atmospheric air, is sufficient to destroy life; and as we see that each human
being consumes per minute nearly four cubic feet of oxygen, and expels
quite that quantity of carbonic gas, &c., it becomes of the most vital
importance that overcrowding should be prevented; and that ventilation
and a good supply of pure air should be made available by every means in
our power.
In illustration of these facts, every one must have read of the horrible
death of the Englishmen who were locked up all night in a close dungeon
at Eort William, Calcutta; 146 individuals were imprisoned in a room 20
feet square with only one small window; and before morning all but 23
had died under the most dreadful of tortures, slowly increasing suffocation.