RESPIRATION. 



353 



cent. ; while, if they were allowed to remain in 

 it until they had become asphyxiated, it con- 

 tained 12'75 per cent. Vierordt, in three 

 experiments, breathed, from 1 h to 3 minutes, a 

 volume of air amounting to 4-27 English cubic 

 inches, and found, on an average, the carbonic 

 acid gas 1'5 per cent, above that contained in 

 air breathed only once. 



The percentage of carbonic acid in the 

 expired air differs at different periods of the 

 same expiration. As the air expelled in the 

 first part of an expiration consists chiefly of 

 that contained in the trachea and upper part 

 ol the air passages, its amount of carbonic 

 acid gas must necessarily be smaller than that 

 expelled at a later period of the expiration. 

 Allen and Pepys found the carbonic acid gas 

 in the first and last portions of air in a deep 

 expiration to differ as widely as 3'5 and 9'5 

 per cent. Dalton states that while the ave- 

 rage carbonic acid in an ordinary expiration is 

 4 per cent., the last portion of a forced ex- 

 piration contains 6 per cent. Vierordt divided 

 the air of an ordinary expiration as far as 

 possible into two equal parts, and in tsventy- 

 one experiments ascertained that while the 

 average quantity of carbonic acid in the whole 

 expiration was 4'48, the first half contained 

 3-72 per cent., and the last half 5'44 per cent. 

 We have already seen, that Vierordt concludes 

 from his experiments that the air, after a 

 sojourn of about 40 seconds in the respiratory 

 apparatus, has the same percentage of car- 

 bonic acid gas in the different parts of the 

 lungs and air passages, 



From the above details, it must be obvious 

 that nearly all the attempts made to estimate 

 exactly the average quantity of carbon evolved 

 in the form of carbonic acid gas from the body 

 in the 24 hours are entitled to very little con- 

 fidence. The greater number of these are 

 founded on a few experiments performed upon 

 one or a very small number only of indi- 

 viduals in a state of rest, and upon the result 

 of a few respirations in some cases performed 

 under constraint. The estimate of the amount 

 of loss of carbon in the 24 hours from the 

 lungs and external surface of the body, based 

 upon the direct method of experiment, in 

 which the greatest number of the circumstances 

 that influence the evolution of carbonic acid 

 gas from the lungs were taken into account, is 

 undoubtedly that of Scharling, though this 

 even must be regarded as an approximation 

 only to the truth. Suppose we take the 

 average estimate of the two adult males be- 

 tween 28 and 35 years of age for the 24 hours, 

 as given by Scharling *, the loss of carbon by 

 the lungs and skin is 3543'13 Troy grains, or 

 7-382 oz. Troy, f Liebig J has endeavoured 



* Vide table given in p. 350. 



f The estimates of the average loss of carbon, in 

 the form of carbonic acid gas, from the lungs in the 

 twenty-four hours by other experimenters, differ con- 

 siderably. Lavoisier and Seguin estimated the loss 

 of carbonic acid gas at 14,930 cubic inches, which 

 they believed -would yield 2770304 grains Tmv; 

 Messrs. Allen and Pepys at 39,534 cubic inches 'of 

 carbonic acid gas, containing rather more than 1 1 

 oz. Troy of carbon ; and Mr. Coathupe at 10,666 cubic 



VOL. IV. 



to ascertain the quantity of carbon lost at the 

 lungs and skin in the 24 hours by the indirect 

 method of research, which he maintains to be 

 by far the most trust-worthy. He proceeded 

 to ascertain the quantity of charcoal in the 

 daily food and drink of a body of soldiers, and 

 after deducting the comparatively small quan- 

 tity of this substance that passes off' in the 

 faeces and urine, the remainder was taken as 

 the amount of carbon that unites with oxygen, 

 and escapes in the form of carbonic acid gas 

 by the lungs and skin. From the data thus 

 obtained he calculates that an adult male, 

 taking moderate exercise, loses 13'9 oz. of 

 carbon daily by the lungs and skin ; and that 

 37 oz. of oxygen gas must be daily absorbed 

 from the atmospheric air for the purpose of 

 converting this charcoal into carbonic acid 

 gas. From similar experiments upon the in- 

 mates of the Bridewell at Marienschloss (a 

 prison where labour is enforced), he calculates 

 that each individual lost in this manner 10'5 

 oz. of carbon daily ; while in another prison, 

 where the inmates were deprived of exercise, 

 this loss amounted only to 8'5 oz. daily. * 

 Allowing that this indirect method of research 

 is more accurate than the direct, a point 

 which we are not at present prepared to de- 

 termine, the accuracy of the data upon 

 which Liebig's inferences rest regarding the 

 quantity of carbonic acid exhaled from the 

 lungs and skin in an adult using moderate 

 exercise, has been called in question by Schar- 

 ling. -j- He endeavours to prove, by an ana- 

 lysis of the food and drink allowed to the 

 sailors on board of his Danish Majesty's vessels 

 of war, that the whole carbon taken daily 

 into the body of each of these individuals 

 must be somewhat less than 10^ oz.; yet 

 these sailors are subjected to harder work than 

 ordinary seamen. J 



The quantity of carbonic acid gas evolved 

 from the body in respiration varies greatly in 

 the different divisions of the animal kingdom. 

 It is greater in birds, in proportion to their 

 bulk, than in the cold-blooded vertebrata, and 

 btill smaller in the invertebrata, with the ex- 

 ception of insects. The ascertainment not 



feet of carbonic acid gas, yielding 2386-27 grains, or 

 5-45 oz. avoirdupois. Vierordt, from numerous ex- 

 periments on himself, ascertained that when in a 

 state of rest the quantity of carbonic acid gas ex- 

 haled from the lungs per minute was for the maxi- 

 mum 452 cubic centimetres (27-572 Eng. cub. in.X 

 for the minimum 177 cub. cent. (10797 Eng. cub. in.), 

 and for the average 261 cub. cent. (12-261 Eng. cub. 

 in.), so that the relation of the minimum and maxi- 

 mum was 100 : 255. If the quantity of carbonic 

 acid evolved from the lungs differs so much at dif- 

 ferent times in the same individual in the minute, 

 and is so materially influenced by the varying con- 

 ditions of the body, how ditlirult must it be to 

 ascertain the average quantity during the twenty- 

 four hours. 



J Animal Chemistry, &c., edited by Dr. Gregory, 

 p. 13 ; 3rd edit. 1846. 



* Opus cit. p. 46. 



f Annalen der Chemie und Pharmacie, vonWoh- 

 ler und Liebig, Band Ivii. S. 1. 1846. 



t Opus cit. p. 9. 



The results of the various experiments upon 



A A 



