396 . OF RESPIRATION. 



the lungs, the exhalation of Carbonic acid through the skin may undergo a 

 considerable increase ; for we find a similar disposition to vicarious action in 

 other parts of the excreting apparatus. There is also evidence that the 

 interchange of gases between the air and the blood, through the skin, has 

 an important share in keeping up the temperature of the body (chap, xii); 

 and we find the temperature of the surface much elevated in many cases of 

 pneumonia, phthisis, etc., in which the lungs seem to perform their function 

 very insufficiently. 



314. The total amount of Carbonic acid daily given off from the Skin and 

 Lungs may be estimated in another mode, namely, by determining the total 

 amount of Carbon contained in the ingesta, and the amount excreted in other 

 ways, making allowance for the difference in weight (if any) of the body. 

 In this mode, Prof. Liebig came to the conclusion, that the average amount 

 of carbon exhaled by soldiers in barracks was 13.9 oz. (Hessian), or very 

 nearly 14 oz. troy. From similar collective observations upon the inmates 

 of the Bridewell at Marienschloss (a prison where labor is enforced), he cal- 

 culated that each individual exhaled"10.5 oz. of Carbon daily in the form of 

 Carbonic acid ; while in a prison at Giessen, whose inmates are deprived of 

 all exercise, the daily average was but 8.5 oz. 1 A very exact estimate, 

 though based on more limited data, was made by M. Barral, 2 who experi- 

 mented upon himself (set. 29) in winter (A) and in summer (B), upon a boy 

 6 years old (c), upon a man 59 years old (D), and upon an unmarried woman 

 of 32 years (E). The following table gives the results which he obtained, 

 from an average of five days, in regard to the disposal of the Carbon of the 

 food ; those which relate to its Nitrogen, Hydrogen, and Oxygen will be 

 noticed subsequently ( 317, 318). 



Carbon excreted. 

 Weight of Body. Carbon of Food. In F;eces. In Urine. By exhalation. 



A, 104.5 Ibs. 565Klgrs. 236.2 e^rs. 234.6 grs. 5183.3 grs. 



B, " 4090.9."" 137.4 "' 211.5 " 5741.1 " 



C, 33. ". 23823 " 1-49.7 " G7.9 " 2164.7 " 



D, 129.1 " 5123.0. " 210.0 " 327.3 " 45857 " 



E, 134.6 " 4520.8 " 64.8 " 21G.1 " 4239.9 " 



Thus the average amount of the Carbon daily consumed in pulmonary and 

 cutaneous exhalation by M. Barral himself, was in winter 5183.3 grains, or 

 10.8 oz. troy; whilst in, summer it was but 3741.1 grains, 7.8 oz. troy; this 

 difference is quite conformable to what might have been anticipated from 

 the results of a different mode of experimenting ( 311, i) ; and it throws 

 some light on the discrepancies in the results of other measurements, to find 

 that the seasonal variation is scarcely less than one-third of the mean be- 

 tween these two amounts. The other results correspond closely with the 

 statements of MM. Audral and Gavarret, in regard to the higher proportion 

 of Carbonic acid exhaled (as compared with the bulk of the body) by chil- 

 dren, and the smaller proportion thrown off by men advanced in years, and 

 by women. In some experiments made on himself in Petteukofer's apparatus, 

 Itanke (weighing 161 Ibs.) found that when at rest and fasting, 10,190 grains 

 of Carbonic acid or 2779 grains of Carbon were eliminated in twenty-four 

 hours by the Skin and Lungs, whilst with as full a diet as possible the 

 amount was 13,278 grains of Carbonic acid, or 3621 grains of Carbon. 



315. It is not only by an oxygenated atmosphere that the removal of Car- 

 bonic acid from the blood may be effected. For although it was formerly 

 supposed that the exhaled Carbonic acid is generated in the lungs by the 



combination of atmospheric oxygen with the carbonaceous matters of the 



* 



1 Op. cit., p. 46. * Ann. de Chim. et de Phys., torn. xxv. 



