4306. Because the fewer the inhabitants the less carbonic acid will be exhaled; and thus country people inhale pure oxygen, instead of air impregnated with the narcotic poison, called carbonic acid gas.
4307. Why do trees and flowers help to make country air wholesome?
4308. 1. Because trees and flowers absorb the carbonic acid generated by the lungs of animals, putrid substances, and other noxious exhalations: and 2. Trees and flowers restore to the air the oxygen which has been inhaled by man and other animals.
4309. Why is the air of cities less wholesome than the country air?
4310. 1. Because there are more inhabitants to vitiate the air: 2. The sewers, drains, bins, and filth of a city, very greatly vitiate the air: 3. The streets and alleys prevent a free circulation: and 4. Besides all this, there are fewer trees to absorb the excess of carbonic acid gas, and restore the equilibrium.