4. Therefore the air contained in the lungs is 114 times the bulk of the blood presented, while the weight of the blood so presented is 7½ times as great as the weight of the air contained.
5. In one minute of time the fresh air inspired amounts to 616⅓ cubic inches, or as nearly as may be 18 pints, weighing 190½ grains.
6. In one hour the quantity inspired amounts to 1066⅔ pints, or 2 hogsheads, 20 gallons, and 10⅔ pints, weighing 23¾ ounces and 31 grains.
7. In one day it amounts to 57 hogsheads, 1 gallon, and 7¼ pints, weighing 571½ ounces and 25 grains ([454]).
8. To this volume of air there are presented for aëration in one minute of time 144 ounces of blood, in volume 259½ cubic inches, which is within 18 cubic inches of an imperial gallon.
9. In one hour 540 pounds avoirdupois, measuring 449¼ pints, or 1 hogshead and 1¼ pints;—and
10. In the twenty-four hours, in weight 12,960 pounds; in bulk 10,782½ pints, that is, 24 hogsheads and 4 gallons.
11. Thus, in round numbers, there flow to the human lungs every minute nearly 18 pints of air (besides the 12 pints constantly in the air vesicles) and nearly 8 pints of blood; but in the space of twenty-four hours, upwards of 57 hogsheads of air and 24 hogsheads of blood.
430. Provision cannot have been made for bringing into contact such immense quantities of air and blood, unless important changes are to be produced in both fluids; and accordingly it is found that the air is essentially changed by its contact with the blood, and the blood by its contact with the air.
431. Chemistry has demonstrated the changes effected in the air. Common atmospheric air is a compound body, consisting of pure air and of certain substances diffused in it. Pure air is composed of two gases, azote and oxygen, always combined in fixed proportions. The substances diffused in pure air, and which are in variable quantity, are aqueous vapour and carbonic acid gas. These latter substances form no part of the chemical agents essentially concerned in the process of respiration. The only constituents of the air which are essentially concerned in the process of respiration are the two gases, azote and oxygen, the union of which, in definite proportions, constitutes pure air. But of these two gases each does not perform the same part in the function of respiration, nor is each equally necessary to the support of life.