4301. How is the air of a room affected thus by a crowd?
4302. The elements of the air (inhaled by the breath) are separated in the lungs;—the oxygen is converted in the blood into carbonic acid; and the carbonic acid (together with the nitrogen) is then thrown off by the breath into the room.
4303. Why is country air more pure than the air in cities?
4304. 1. Because there are fewer inhabitants to vitiate the air: 2. There are more trees to restore the equilibrium of the vitiated air: and 3. The free circulation of air keeps it pure and wholesome; in the same way as running streams are pure and wholesome, while stagnant waters are the contrary.
4305. Why does the scantiness of a country population render the country air more pure?