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CHAPTER II.

THE MACHINERY OF THE BREATHING APPARATUS.

A ruLL explanation of the anatomy of the breathing organs is unnecessary here. I will content myself with dealing only with the mechanism involved, briefly outlining the functions which occur during the respiratory proccss, with a vicw to correcting some common errors which are prevalent concerning the matter.

Fig. 4 shows the human trunk opened in front so that most of the internal organs are visible, and Fig. 5 givcs a skcleton-like side-view. The whole inner cavity is divided by a hori/.ontal, but dome-shaped, partition-wall (the dia-phragm) into an upper part (the thoracic compartment), containing the lungs and hcart, and a lower part (the ab-dominal compartment), containing the liver, gall-bladder, stornach, kidneys, intestines, etc. No w it is obvious that the morę the thoras is enlargcd and expanded in various directions, the morę fnlly can the lungs, by inhalation, be inflated with fresh air, rich in oxygen. And, on the other hand, the morę the thorax, during exhalation, can be contracted and narrowed, the greater amount of foul air, containing carbonic acid, that will be expelled from the lungs.

What Constitutes a Respiration ?

One inhalation or inspiration, and one exhalation or expiration, constitutes one breath, or respiration. Inhalation and exhalation will always follow altemately upon each

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