CHAPTER III.

25. What is oxygen?

Oxygen is one of the most widely diffused of the elementary substances. It is a gaseous body.

"Stand in awe and sin not: commune with your own heart upon your bed and be still"—Psalm iv.

26. Why do persons who are walking, or riding upon horseback feel warmer than when they are sitting still?

Because as they breathe more rapidly, the combustion of the carbon in the blood is increased by the oxygen inhaled, and greater heat is developed.