460. Since it appears to be a general truth that one quarter of the air respired is decomposed, and that the volume of air continually present in the lungs is sufficient for that consumption of oxygen which is requisite in 160 seconds of time, _if that volume be_, as is apparent, 48 _times the quantity decomposed_ out of a single respiration, no error in the quantity of oxygen consumed in the twenty-four hours, which we have assumed, will affect the time of 160 seconds. For there being 18 × 60 × 24 respirations, and 60 × 60 × 24 seconds of time in the twenty-four hours, the 48th part of the first, and the 160th part of the last product is equally the 540th part of the whole, whatever it may be. 461. But if the time in which a circuit of the blood is performed be, as is most evident, identical with the time in which the whole volume of air in the lungs is decomposed, and if such period of time were, as the old observers have assigned, 150 seconds, then it would follow that only 45 times the quantity of air decomposed at a breath is present in the lungs, amounting to 385¼ cubic inches, and that the whole blood in the body is 24 ounces less than on the supposition of 160 seconds, that is to say, only 360 ounces, or 22½ pounds avoirdupois. Because the 45th part of 18 × 60 × 24 is the same as the 150th part of 60 × 60 × 24; in each it is the 567th part of the whole. 462. From the whole of these observations and calculations the following general results are deduced:— 1. The volume of air ordinarily present in the lungs is very nearly twelve pints (449). 2. The volume of air received by the lungs at an ordinary inspiration is one pint (422). 3. The volume of air expelled from the lungs at an ordinary expiration is a very little less than one pint (456). 4. Of the volume of air received by the lungs at one inspiration, only one-fourth part is decomposed at one action of the heart (447). 5. The fourth part of the volume of air received by the lungs at one inspiration, and decomposed at one action of the heart, is so decomposed in the five-sixth parts of one second of time (429.3). 6. The time in which a circuit of blood is performed is identical with the time in which the whole volume of air in the lungs is decomposed (461). 7. The whole volume of air decomposed in twenty-four hours is 221,882 cubic inches, exactly 540 times the volume of the contents of the lungs; 160 seconds being also exactly the 540th part of the number of seconds in twenty-four hours (450). 8. The quantity of the blood that flows to the lungs to be acted upon by the air at one action of the heart is two ounces (425). 9. This quantity of blood is acted upon by the air in the five-sixth parts of one second of time (429.3). 10. One circuit of the blood is performed in 160 seconds of time. Three circuits are performed every eight minutes; 540 circuits are performed in the twenty-four hours (453).