* * * * *
QUESTIONS FOR THE FORMULA.
1. What are the lungs?
2. Describe the lungs.
3. How do you breathe?
4. Why can you not live without breathing?
5. What is necessary if you would have healthy lungs?
* * * * *
THE AIR AND THE LUNGS.
The air which enters through the nose and mouth passes into a tube of
muscles and ring-like pieces of cartilage. The upper part of this tube is
the voice-box or _larynx_, covered by a spoon-shaped lid which closes when
we swallow; the lower part is the _trachea_, and the two parts are the
windpipe. The trachea divides into two branches, _the bronchial tubes_, one
for each lung. These tubes divide again and again like the branches of a
tree, and end in exceedingly small sacs or bags. The air in these sacs, or
air-cells, gives _oxygen_ to the blood in the tiny blood-vessels of the
lungs and takes from them the poison, _carbonic-acid gas_, water, and
impurities, which it carries back through the windpipe into the outside
air.
* * * * *
QUESTIONS ON THE LUNGS AND RESPIRATION.
Of what are the lungs composed?--"Of a soft, fleshy substance, full of
small air-cells and tubes.
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