RESPIRATION. 



The only other gas to which the death of animals, in 

 thefe circumftances, can be afcribej, is carbonic acid, which, 

 however, when formed by refpiration, does notfeem deftruc- 

 tive to animal life. Dr. Goodwyn obferves, that \ 

 the fame air is breathed feveral times, fo as to increafe the 

 quantity of carbonic acid, its noxious operation is to be 

 attributed not to the prefer.ee of this acid, but to the defi- 

 ciency or abfence of oxygen gas (Connection of Life, &c. 

 p. 66.); and when Spallanzani, by means of an alkaline 

 fubltance, abftrafted this acid as foon as formed by th 

 fpiration of birds and quadrupeds, he did not find that 

 lived longer in a given bulk of air than when it was fufl 

 to remain. (Memoirs on Refpiration, p. 318.) Dr. 

 Higgins obferves, that debility, convulfions, and death, 

 follow the fuccefiive diminution of the oxygen gas of the 

 air in refpiration, long before the whole of that ga 

 fumed, although the carbonic acid that is generated be, in 

 the mean time, carefully withdrawn. (Minutes of a Society, 

 p. 160.) Indeed, we might in this, as in former examples, 

 be led to fuppofe, that neither the carbonic acid formed in 

 refpiration, nor the nitrogen gas employed in that procefs, 

 would exert any pofitively deftru&ive operation on the ani- 

 mal powers, fincc both of them mutt, at all times, neceffa- 

 rily beprefent in the fyftem; and feeing, moreover, that the 

 abilraction of oxygen gas alone is fufficient to account for 

 the fatal effects which enfue, it mud be deemed unnecefiary 

 to refort to the fuppofed agency of any lubordinate caufe. 

 Inquiry, &c. § 127 — 130. 



Quantity of Carbonic Acid produced. — Having afcertained 

 the proportion of oxygen which is confumed in refpiration, 

 it next remains for us to determine the quantity of carbonic 

 acid gas which is produced. It appears that Dr. Black 

 Jirll demon ftrated its exillence in air emitted from the lungs, 

 and that Lavoifier afterwards examined it with more accu- 

 racy, and found that the air, in which an animal had ex- 

 pired, contained about one-fixthof its bulk of carbonic acid 

 gas. (Acad, des Sciences, 1777.) In the experiment which 

 this philofopher performed with a more perfect apparatus, 

 upon a guinea pig confined in oxygen, the carbonic acid 

 amounted to nearly one-fifth of the bulk of the whole air 

 employed, when the animal had been detained in the appa- 

 ratus until the air was reduced into a ftate no longer fit for 

 refpiration. (Annates de Chimie, t. 5. p. 26 1, et feq.) 

 Thefs experiments, however, only prove what proportion 

 of carbonic acid gas will render air incapable of Supporting 

 life, without acquainting us with the quantity of this gas 

 produced under the ordinary circumftances of refpiration. 



M. Jurine of Geneva, appears to have been the firft 

 who attempted to calculate the abfolute quantity of car- 

 bonic acid formed by the refpiration of man ; he imagined 

 that it conftituted about one-tenth part of the air emitted 

 from the lungs. ( Eiicycl. Method. Medecine, v. 1. p. 494.) 

 Dr. Menzies inftituted a iet of experiments to difcovcr the 

 abfolute quantity generated in a given time ; he infers from 

 them, that ,', th part of air which has been once refpircd, is 

 carbonic acid, and cftimatcs, that a man, in 24 hours, fends 

 out from the lungs 51,840 cubic inches, or nearly 4lbs. 

 troy ; but this ettimatc is probably over-rated. Kllay, 



P- *°- 



Tin- circumftances which have been already pointed out, 



as influencing the confumption of oxygen, have at halt as 

 powerful an effect upon the produftion of carbonic acid gas. 

 Accordingly wc fhall find the calculations of the moll accu- 

 rate experimenters upon this fubjedt fo widely different from 

 each other, that it feems fcarcely poffible to arrive at any 

 tolerable degree of certainty. 



M. M. Lavoificr and Seguin, in their firft memoir of 



1789, eftimate the average quantity of carbonic acid gas, 

 formed by a man in 24 hours, at 17720.89 grains troy ; in 

 their fubiequent memoir, publifhcd in the following year, 

 this quantity is diminilhed 108450.24 grains; and in the 

 eulogy of Lavoifier by La Place, it is Hated, that Lavoi- 

 fier, in his laft experiments, reduced it ft ill lower, to 7550.40 

 grains. Mr. Davy, on the contrary, whofe experiments 

 feem to have been performed with great exadnefs, though 

 a lefs complicated apparatus than that employed by the 

 French chemilts, fuppofes the carbonic acid formed in 24 

 hours to amount to 17811.3S grains (Researches, p. 434.), 

 a quantity which is not very different from that firll an- 

 nounced by Lavoificr. 



Mr. Murray found that he expired 265 cubic inches of air 

 in 30 feconds, and he difcovered in this 16.57 cubic inches of 

 carbonic acid. Making a deduction for the fmall quantity 

 of this acid contained in the infpired air, lie affumes 16 cu- 

 bic inches as the quantity formed by refpiration in 30 fe- 

 He calculated the quantity of oxygen confumed at 

 19 cubic inches: the ratio, therefore, between the calcu- 

 lated quantity of oxygen confumed, and the actual quantity 

 of carbonic acid formed, was as 100 to 84.5. Sylt. ofChe- 

 miftry, v. 4. p. 494. 



Meilrs. Allen and Pepys conclude from their experiments, 

 that '. I. eric air expelled from the lungs ufually con- 



tains from 8 to 8.5 per ecu/, of carbonic acid, and that the 

 proportion of acid in no cafe exceeds jo per cent. They 

 eltimate the quantity of acid thrown off in 11 minutes at 

 302 cubic inches, which ib abont 27.45 P er minute; and 

 tuppofiMg the production uniform for 24 hours, the total 

 quantity in that period would be 39,534 cubic inches, weigh- 

 ing 18,683 t, rl ' a ' 113 ' '"' rather more than 11 oz. troy. Phil. 

 Tranf. 1808. 



If a larger quantity of air be paffed through the lungs in 

 a given time, more carbonic acid is formed, but it (till pre- 

 ferves the fame ratio to the other component parts of the ex- 

 pired mais. Thus, 3300 cubic inches of air were infpired 

 by one perfon in 5^ minutes, and as each 100 parts contained 

 8.5 of carbonic acid, the whole acid formed in this time was 

 281.42 cubic inches. The lirlt and laft portions of afingle 

 expiration differ coniiderably in their proportions of car- 

 bonic acid, becaufe the former conlifts principally of air 

 contained in the fauces, trachea, and its larger branches, 

 while the latter come6 from the air-cells themfclvcs. In 

 fmall quantities of the firft portions, given off by natural 

 and eafy expirations, the carbonic acid formed from three to 

 five per cent. When an expiration was made as complete as 

 pofiible, the utmolt efforts being employed to prefs the air 

 out of the lungs, 204 cubic inches were expelled, and the 

 proportion of carbonic acid was 9.5. Now as the firft por- 

 tions contain only from three to five per cent., the laft mull 

 have contained more than the average, or 9.5. When 

 300 inches of atmofpheric air were repeatedly breath d, un- 

 til the laborious ftate of refpiration compelled the opei 

 to defilt, ioo parts of the expired air contained 9.5 carbonic 

 acid, 5.5 oxygen, and 85 azote. When a fimilar trial 

 repeated until the operator became infenfible, 100 parts of 

 the air contained 10 carbonic acid, 4 oxygen, and 86 azote. 

 (Phil. Tranf. 180S.) When 3260 <.'.:<• ■ ; of gas, 



confiHing of 97.5 oxygen, and 2.5 azote in ico parts, were 

 refpired tor 9 minute II ' the expired air It 



lured 3193 inches, and contained, in ioo parts, 1 1 carb 

 acid, 83 oxygen, 6 azote. 1 1. re, therefore, ^7.64 cubit 

 inches of carbonic acid 9 ed from the lungs in one 



minute by the fame individual, who produced 27.4; fir mi- 

 nute, when he breathed common air. In anothei u 

 3420 cubic inches 1 for 7' a 



G 2 



