ELIMINATION OF NITROGEN. 827 



13 cubic inches of carbonic acid are exhaled per minute, which would 

 be equal to a total of 5J oz. av. of carbon thrown off by the lungs in 

 twenty-four hours. The calculations of Valentin and Brunner, Davy, 

 Allen, Pepys, and Lavoisier, agree closely, yielding, as a general re- 

 sult, 8 oz. of carbon excreted by the lungs in twenty-four hours. An- 

 dral and Gavarett estimated the daily quantity at 9 oz. ; Vierordt says 

 that it varies from 5 to 8 oz. Dr. E. Smith found, as an average of 

 eight experiments, the daily quantity, in a state of rest, in four men, 

 whose mean height was 5 feet 9} inches, to be 7.144 oz. ; the extremes 

 were 5.6 oz. and 7.85 oz. With an ordinary amount of exercise, he 

 estimates the quantity at about 8J oz., and in a working man fully 

 engaged in labor, at rather more than 11J oz. 



Adopting as a basis of calculation, the estimate already given at 

 p. 821, viz., of 300 cubic feet, or 518,400 cubic inches, as the total 

 quantity of air respired in twenty-four hours, by an average-sized adult 

 male, 5 feet 6J inches in height, allowing for the effects of work in 

 the day and the influence of repose at night, and, moreover, calcula- 

 ting that the average quantity of carbonic acid in the air when ex- 

 pired is 4 per cent., then 20,736 cubic inches of carbonic acid would 

 be given off in the twenty four hours. As 100 cubic inches of car- 

 bonic acid gas weigh 47.26 grains, this quantity would weigh about 

 9800 grains, which would contain 2672 grains, or rather more than 

 6 oz. av. of carbon. This is perhaps a fair calculation for a man of 

 medium size, not engaged in any special exercise or labor. 



Elimination of Nitrogen. The nitrogen of the atmosphere, which 

 serves to dilute the oxygen, is, to a slight extent, absorbed by the 

 blood, for that fluid always contains nitrogen in a state of solution. 

 Nitrogen, however, is also given off from the blood through the breath; 

 and the balance appears to be rather in favor of the process of elimi- 

 nation. The quantity thus thrown off by warm-blooded animals, is so 

 minute as never to exceed g^th part of the oxygen consumed (Vie- 

 rordt) ; sometimes it is less than yj^th part. (Regnault and Reiset.) 

 The source of this small excess in the nitrogen exhaled, was at one 

 time supposed to be the nitrogenous aliments, the quantity of nitrogen 

 excreted by the kidneys, skin, and intestines, being supposed to be 

 less than that taken in the food. The quantity of nitrogen not ac- 

 counted for in the renal, cutaneous, and intestinal excretions, has 

 been said to be equal to ^gth of the oxygen consumed in an adult, 

 which nearly agrees with the estimate of Regnault and Reiset above 

 mentioned. But, according to Voit and others, however, all the nitro- 

 gen of the food which is actually subjected to metamorphosis in the 

 blood, is accounted for in the nitrogenous constituents of the urine. 

 The minute and unimportant excess in the expired air may, therefore, 

 be derived from the atmospheric air, which is swallowed with the 

 saliva, food, and drink, and is taken up by venous absorption ; its 

 oxygen being utilized in the blood, the nitrogen escapes through the 

 walls of the pulmonary capillaries and the air-cells, into the breath. 

 In favor of this view, it may be added, that the decomposition of ni- 

 trogenous substances in the system, so as to yield free nitrogen, is 

 unknown ; that in starving animals, which probably swallow less air, 



