SUMMARY.

1. Our bodies need air, just as a candle or a fire does.

2. A small animal shut up in a close jar soon dies for want of air. We
need the oxygen which the air contains.

3. Oxygen causes a sort of burning in our bodies.

4. The burning in our bodies keeps us warm, and destroys some of the
waste matters.

5. The breathing organs are the windpipe and bronchial tubes, the
voice-box, the epiglottis, the nostrils, the soft palate, the lungs, the
air-cells, the pleura, the diaphragm, and the chest walls.

6. When we breathe we use our lungs like a pair of bellows.

7. A man's lungs hold nearly one and a half gallons of air.

8. In ordinary breathing we use less than a pint of air, but when
necessary we can use much more.

9. The air we breathe out contains carbonic-acid gas and another
invisible poison.

10. A candle will not burn in air which has been breathed, and animals
die when confined in such air.

11. The lungs purify the blood. While passing through the lungs, the