tion of the respiratory organs. Stays and corsets, and
tight vests and waistbands, operate most injuriously, compressing as
they do the thoracic cavity, and interfering with the healthy dilation
of the lungs.

The admirable harmony established by the Creator between the various
constituent parts of the animal frame, renders it impossible to pay
regard to the conditions required for the health of any one, or to
infringe the conditions required therefor, without all the rest
participating in the benefit or injury. Thus, while cheerful exercise in
the open air and in the society of equals is directly and eminently
conducive to the well-being of the muscular system, the advantage does
not stop there, the beneficent Creator having kindly so ordered it that
the same exercise shall be scarcely less advantageous to the important
function of respiration. Active exercise calls the lungs into play,
favors their expansion, promotes the circulation of the blood through
their substance, and leads to their complete and healthy development.
The same end is greatly facilitated by that free and vigorous exercise
of the voice, which so uniformly accompanies and enlivens the sports of
the young, and which doubles the benefits derived from them considered
as exercise. The excitement of the social and moral feelings which
children experience while engaged in play is another powerful tonic, the
influence of which on the general health ought not to be overlooked; for
the nervous influence is as indispensable to the right performance of
respiration as it is to the action of the muscles or to the digestion of
food.

The regular supply of pure fresh air is another essential condition of
healthy respiration, without which the requisite changes in the
constitution of the blood, as it passes through the lungs, can not be
effected. To enable the reader to appreciate this condition, it is
necessary to consider the nature of the changes alluded to.

It is ascertained by analysis that the air we breathe is composed
chiefly of the two gases _nitrogen_ and _oxygen_, united in the ratio of
four to one by volume, with exceedingly small and variable quantities of
carbonic acid and aqueous vapor. No other mixture of these, or of any
other gases, will sustain healthy respiration. To be more
specific--atmospheric air consists of about seventy-eight per cent. of
nitrogen, twenty-one per cent. of oxygen, and not quite one per cent. of
carbonic acid. Such is it