Because it combines with the carbon of the blood, and forms carbonic acid gas.
"Be not as the horse, or as the mule, which have no understanding: whose mouth must be held with the bit and bridle."—Psalm xxxii.
6. Why is this combination necessary?
Because we are so created that the substances of our bodies are constantly undergoing change, and this resolving of solid matter into a gaseous form, is the plan appointed by our Creator to remove the matter called carbon from our systems.
7. Why do our bodies feel warm?
Because, in the union of oxygen and carbon, heat is developed.