ared with much care, for so great a misuse of the mind
as cramming implies.

Breathing is essential for life. The oxygen of the air is, of all
food-stuffs, the most important. Without it a mammal will perish in
less than three minutes; hence there is no need of the body so urgent
as that of oxygen. It is also of great moment that the waste--the
carbon dioxide, or carbonic acid gas--should be got rid of rapidly;
nevertheless, it is not this gas which kills when the air-passages are
closed, though it is highly deleterious. The body is a sort of furnace
in which combustions are continually going on, and oxygen is as
essential for these as for the burning of a candle, and the products
are in each case the same.

Whether the voice-user respires, like others, to maintain the
functions of the body, or whether he employs the breathing apparatus
to produce sound, it is to be borne in mind that he uses the same
physical mechanisms, so that the way is at once clear to consider the
anatomy and physiology of the breathing organs.

It has been already pointed out that respiration is in all animals, in
the end, the same process. The one-celled animal and the muscle-cell
respire in the same way, and with the same results--oxidation,
combustion, and resulting waste products. In the animal of complicated
structure special mechanisms are necessary that the essential oxygen
be brought to the blood and the useless carbon dioxide removed. The
respiratory organs or tract include the mouth, nose, larynx, trachea,
bronchial tubes, and the lung-tissue proper or the air-cells.

The mouth, nose, and larynx, in so far as they are of special
importance in voice-production, will be considered later.

The air enters the trachea, or windpipe, through a relatively narrow
slit in the larynx, or voice-box, known as the _glottis_, or _chink of
the glottis_, which is wider when air is being taken in
(_inspiration_) than when it is being expelled (_expiration_). Life
depends on this chink being kept open. The windpipe is composed of a
series of cartilaginous or gristly rings connected together by softer
tissues. These rings are not entire, but are completed behind by soft
tissues including muscle. It follows that this tube is pliable and
extensible--a very important provision, especially when large
movements of the neck are made, during vigorous exercise, and also in
singing and speaking.

The bronchial tubes are the tree-like branches of the trachea,