m a room. It
is successfully used upon all the public school-houses of
Boston. It is now being generally applied to the school-houses
and other public buildings, as well as private dwellings, of
New England.

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512. Why are we insensible to the gradual vitiation of the air of an
unventilated room? 513. What is very important in the building of
every inhabited room? How can a room be well ventilated? 514. What is
said relative to a communication with the external air?

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515. In warming rooms, the hot air furnaces, or box and air-tight
stoves converted into hot air furnaces, should be used in preference
to the ordinary stoves. The air thus introduced into the room is pure
as well as warm. In the adaptation of furnaces to dwelling-houses,
&c., it is necessary that the air should pass over an ample surface of
iron moderately heated; as a red heat abstracts the oxygen from the
contiguous air, and thus renders it unfit to be respired.[17]

[17] Dr. Wyman's valuable work on "Ventilation," and the work of Henry
Barnard, Esq., on "School-house architecture," can be
advantageously consulted, as they give the practical methods of
ventilating and warming shops, school-rooms, dwelling-houses,
public halls, &c.

_Observation_. Domestic animals need a supply of pure air as well as
man. The cows of cities, that breathe a vitiated air, have, very
generally, tubercles. Sheep that are shut in a confined air, die of a
disease called the "rot," which is of a tuberculous character.
Interest and humanity require that the buildings for animals be
properly ventilated.

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515. How should rooms be warmed? What is necessary in the adaptation
of furnaces to dwelling-houses?

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CHAPTER XXVI.

HYGIENE OF THE RESPIRATORY ORGANS, CONTINUED.

516. The change that is effected in the blood while passing through
the lungs, not only depends upon the purity of the air, but the amount
inspired. The quantity varies according to the size of the chest, and
the movement of the ribs and diaphragm.

517. _The size of the chest and lungs can be reduced by moderate and
continued pressure._ This is most easily done in infancy, when the
cartilages and ribs are very pliant; yet it can be effected at more
advanced periods of life, even after the chest is fully developed. For
want of k