PHYSIOLOGY. 
of oxygen gas that difappeared every minute was 3i'6 
cubic inches, and that of carbonic acid produced 26*6 
inches. But one cubic inch of oxygen gas weighs 
0*3474 of a grain, and therefore 31*6 cubic inches will 
weigh 10*97784 grains; again, one cubic inch of carbo¬ 
nic acid weighs 0*476 of a grain, and therefore 26*6 cu¬ 
bic inches will weigh 12*4222 grains. From thefe fafts 
it would feem, that the proportion of carbon in the carbo¬ 
nic acid of refpiration is much lefs than that which 
forms the fame acid in combuftion. For 100 parts of 
carbonic acid, formed by burning.the diamond, contain, 
according to the very accurate refearches of Allen and 
Pepys, (Phil. Tranf. 1807,) 20*72 or 28*81 of carbon: 
and the proportion of carbon in 100 parts of acid is 28*77 
when it is formed from charcoal and oxygen. (Murray’s 
Chemiftry, vol. ii.) 
On no point of the refpiratory procefs are the recorded 
refults of different enquiries more at variance with each 
other, than about the queftion of the change in volume 
of the air, and the amount of that change. At firft, it 
was generally believed, that the refpired air undergoes 
fotne lofs ; and this opinion maintained its ground until 
very lately, although experiments were publilhed, in 
which no fuch lofs was obferved. The molt accurate 
modern refearches are much in favour of the opinion, 
that the bulk of the ntmofphere is not affefied by 
breathing; and this view of the fubjefl: is the molt ge¬ 
nerally entertained in the prefent day. But fome think, 
that, although the volume of the refpired air is not af- 
fe< 5 ted in ordinary natural breathing, it may be altered 
under particular circumltances. The determination of 
the queftion concerning the volume of the air is clofely 
connefted with another refpedling its abforption by the 
blood. We fhall detail the fadis and arguments on both 
Tides, and point out that which has the molt numerous 
and ftrong proofs in its favour. 
The diminution of bulk was early noticed by Boyle, 
who eftimated it at about gSgth of the air employed. 
Mayow, whofe genius enabled him to anticipate fo many 
important difcoveries cf modern chemiftry, confined an 
animal in a glafs vefiel inverted over water, and, by the 
aid ot a fiphon, brought the water on the infide of the 
vefiel to a level with that on the outfide. Having then 
marked the height of the water by pieces of paper af¬ 
fixed to the fide of the veffel, he obferved its gradual 
rife as the animal continued to breathe ; and then, com¬ 
paring the fpace occupied by the air at the commence¬ 
ment of the experiment, with that which it pofleffed 
when the animal ceafed to breathe, he found that it was 
reduced about -j^th part of its bulk. (Tradlat. Quinque, 
p. 104.) In the experiments of Dr. Hales, the degree 
of diminution varied from -j*jth to -^ s th of the air em¬ 
ployed. (Statical Effays, i. 230. ii. 320.) 
Lavoifter, in the firft memoir which he publilhed upon 
refpiration, afcertained the degree of diminution with 
more accuracy, and ftated, that air, when rendered un¬ 
fit to fupport life, was reduced ^gth of its bulk. (Mem. 
- de_ l’Acad. 1777.) The experiments of Dr. Goodwyn 
afforded the fame refult. 
_ In the account which Lavoifier gives of the firft expe¬ 
riment upon the guinea-pig, he found the diminution 
to amount to 0 f the hulk of the air employed ; (Mem. 
de 1 ’Acad. 1780, p. 401.) and in the fecond fet of expe¬ 
riments, the diminution was found to be -J ? part; (An- 
nales de Chimie, tom. v. p. 261.) the greater abforption, 
in thefe cafes, probably depending upon the greater purity 
of the air employed. 
. The general fatt of the diminution of bulk in refpired 
air, has been fince confirmed by Mr. Davy, though the 
exaft degree of abforption varied fo much in his differ¬ 
ent experiments, that it is difficult from them to fix upon 
a quantity which may indicate the ordinary amount of 
this diminution. 
On the other hand, Meffrs. Allen and Pepys, whofe 
experiments afford the ftrongeft arguments againft: a 
V-ol.XX. No. 1373. 
353 
change of volume in the refpired air in natural breath¬ 
ing, met with a different refult when the circumltances 
of the experiment were changed. In their fourteenth 
experiment, 300 cubic inches of atmofpheric air were, 
in the fpace of three minutes, pafled eight or ten times 
through the lungs, until refpiration became extremely la¬ 
borious, and the operator was compelled to defift. On 
analyfing the refpired air, it was found to contain, in 100 
parts, only 5*5 oxygen, 9*5 carbonic acid, and 85 parts 
of nitrogen gas. In the fifteenth experiment, which 
occupied alfo about three minutes, until the operator 
became quite infenfible, the fame quantity of air was em¬ 
ployed, and afforded, by analyfis, nearly the fame refults ; 
for it contained, in 100 parts, 4 of oxygen, 10 of carbo¬ 
nic acid, and 86 of nitrogen. In the former experiment 
we obferve, therefore, an increafe of 6 parts of nitrogen, 
and a lofs of 6 parts of oxygen; and in the latter, the 
oxygen had loft 7 from 21, and the nitrogen had gained 
7 upon 29. (Phil. Tranf. 1808. p. 260.) 
Among the earlielt experiments of Dr. Prieftley on 
refpiration is one in which he confined a moufe in ajar 
containing a given quantity of air, which was inverted 
over mercury. The animal was fuffered to remain two 
or three days after he had died, in which time there was 
no fenfible diminution of the air ; but, on palling lime- 
water into the jar, the air was diminilhed -Jg-th P art °f its 
bulk ; and when, in a fubfequent experiment, the reli- 
dual air was agitated in water, it was reduced between 
one-fifth and one.-fixth of the whole. (Obf. on Air, vol. 
v. p. 112.) Dr. Crawford found alfo, that, when tlie ex¬ 
periment was made over mercury, the diminution was 
not fenfible; but that, if water of potaffa was added to 
the relidua! air, it became mild, and the air was dimi¬ 
nilhed in the fame degree as if the experiment had been 
made over water, or nearly one-fifth of its bulk. (On 
Animal Heat, p. 146.) The variations in thefe refults, 
compared with thofe before enumerated, arife, no doubt, 
from the more or lefs complete attraction of the carbonic 
acid by the fluids over which the experiments were made; 
and, from the whole of them, we may collect, that when 
mercury is employed, which has no attraction for carbo¬ 
nic acid, the diminution is hardly fenfible ; but that, 
when this acid is completely abftraCted by an alkaline 
fluid, the lofs of bulk amounts nearly to one-fifth of the 
whole air employed. This inference correfponds very 
exaCtly with what occurs in vegetation, and in the refpi¬ 
ration of the inferior animals. 
In the year 1806, Mr. Dalton’s attention was directed 
to this fubjeCt ; and he fatisfied liimfelf, by numerous 
experiments, that the bulk of carbonic acid, formed in 
refpiration, was exaCtly equal to that of the oxygen gas 
confumed. On repeating thefe experiments, Dr. Thom- 
fon obtained, in fome cales, nearly the fame refults ; but, 
upon the whole, the bulk of oxygen that difappeared was 
fomewhat greater than that of the carbonic acid formed. 
The difference, however, varied conliderably, and kept 
pace with the diminution in the whole bulk of air; 
whence he conliders it tc arife from the abftraftion of a 
part of the air by fome other way than by refpiration : 
and, if this be allowed for, he believes the bulk of acid 
produced to be precifely equal to that of oxygen gas 
loft. Hence, fays he, this oxygen muft be changed into 
carbonic acid in the lungs; for oxygen gas, when 
changed into carbonic acid, does not lenlibly alter its 
bulk. (Syffem of Chemiftry, vol. v.) 
Thele conclulions have been completely confirmed bythe 
very accurate experiments, already noticed, of Allen and 
Pepys. There was a lofs of 23 cubic inches only in 3460 
breathed once,at38refpirations,vvhich occupied 11 minutes. 
In another experiment, 9S90 cubic inches, of which the 
breathing occupied 245 minutes, loft only 18. In fubfe¬ 
quent experiments on the refpiration of aguinea-pig, thefe 
chemifts found, that when 310 cubic inches of atmofpheric 
air were breathed for 25 minutes by this animal, its volume 
experienced no variation whatever; and the portion of 
4 X its- 
