the lungs and skin,
has a deleterious effect on the body._ When this element is vitiated
from the preceding causes, it prevents the proper arterialization, or
change in the blood. For this reason, pure air should be admitted
freely and constantly into work-shops and dwelling-houses, and the
vitiated air permitted to escape. This is of greater importance than
the warming of these apartments. We can compensate for the deficiency
of a stove, by an extra garment or an increased quantity of food; but
neither garment, exercise, nor food will compensate for pure air.

506. _School-rooms should be ventilated._ If they are not, the pupils
will be restless, and complain of languor and headache. Those
unpleasant sensations are caused by a want of pure air, to give an
adequate supply of oxygen to the lungs. When pupils breathe for a
series of years such vitiated air, their life is undoubtedly
shortened, by giving rise to consumption and other fatal diseases.

_Illustration._ A school-room thirty feet square and eight feet high,
contains 7200 cubic feet of air. This room will seat sixty pupils,
and, allowing ten cubic feet of air to each pupil per minute, all the
air in the room will be vitiated in twelve minutes.

_Observation._ In all school-rooms where there is not adequate
ventilation, it is advisable to have a recess of five or ten minutes
each hour. During this time, let the pupils breathe fresh air, and
open the doors and windows, so that the air of the room shall be
completely changed.

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Of the effects of breathing impure air. 505. In preserving health,
what is of greater importance than warming the room? 506. Why should a
school-room be ventilated? Give the illustration.

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507. _Churches, concert halls, and all rooms designed for a collection
of individuals, should be amply ventilated._ While the architect and
workmen are assiduous in giving these public rooms architectural
beauty and splendor, by adorning the ceiling with Gothic tracery,
rearing richly carved columns, and providing carefully for the warming
of the room, it too frequently happens that no direct provision is
made for the change of that element which gives us beauty, strength,
and life.

_Illustration._ A hall sixty feet by forty, and fifteen feet high,
contains 36,000 cubic feet of air. A hall of this size will seat four
hundred persons; by allowing ten cubic feet of air to each person per
minu