PHYSIOLOGY. 
354 
its oxygen, which difappeared, was replaced by an equal 
bulk of carbonic acid. Thefe refults were particularly 
fatisfadlory in their tendency to eftablifh the point, that 
the air undergoes no diminution ; becaufe the time 
which they occupied was more confiderable, and the 
chance of error, therefore, diminilhed. The third trial 
with the guinea-pig occupied one hour: the bulk of the 
atmofpheric air, before the experiment, was 1060 cubic 
inches; after the experiment, 1061; the carbonic acid 
formed 53 cubic inches; the carbonic acid per minute, 
•88 of a cubic inch. (Phih Tranf. 1809, p. 414.) Where¬ 
fore they juftly conclude, that when atmofpheric air 
alone is refpired, no other change is produced in it than 
the fubftitution of a certain portion of carbonic acid gas 
for an equal volume of oxygen. 
Amid this conflict of authorities we can only remark, 
that our opinion agrees with that which denies diminu¬ 
tion in the bulk of the refpired air; the trifling variations 
which have been noticed arifing from the circumflance, 
that, as the animals operated on became exhaufted, they 
were unable to evacuate their lungs of the contained air 
fo perfeflly as before the experiment. 
3.With refpedft to the alterations the blood undergoes du¬ 
ring refpiration, thefe confift merely in a change of the pur¬ 
ple colour, which is feen in the vefl'els tinging the blood to 
the lungs, to a red one obferved in thofe which again carry 
it into the general circulation, and in a flight elevation of 
temperature (fee Dr. Davy’s experiments in Phil. Tranf. 
3814.) which follows the fame tranfmiflion. It appears 
obvious indeed that the change of colour neceffarily im¬ 
plies fome chemical change of conftitution ; but it is fo 
Slight in degree, that we have no ana'tyfis of it. 
If we are correftin reprefenting that the air undergoes 
r.o diminution of volume in breathing, it will follow ne¬ 
ceflarily that no part of it can be abforbed in the lungs. 
This notion of ablorption is not only at variance with 
the refults of the mod accurate diredl experiments, but 
it is alfo repugnant to our knowledge of the ftrudlure of 
the lungs. The finenefs of the abforbing vefl’els, the 
mucus perpetually fmearing the furfaceof the cells, the 
elaftic nature of air itfeif, fo that it neither penetrates 
moift paper, cloth, nor flcin; all demonftrate that no air 
(in its aeriform date) gets into the blood by this route. 
If, indeed, air were taken up by the abforbents, it mud 
pafs to the right fide of the heart, and change the colour 
of the blood there, which does not happen. But if, ei¬ 
ther by the fundlion of ablorption, or by the operation 
of chemical affinity, air did enter into the blood, we may 
furely with reafon demand lome proof of its prefence; 
yet, fays Haller, “Nulla unquam in vivo calido animali 
bulla aeris in fanguine vifa ed.” (Prirnae Lin. § 306.) 
This opinion is confirmed by the diredt experiments of 
Dr. Darwin; for, having inclofed a portion of the jugu¬ 
lar vein of a (heep between tw r o ligatures, it was cut 
out, dripped of its adhering cellular membrane, and then 
thrown into aglafs of water of temperature ioo°, hand¬ 
ing under the receiver of an air-pump. It at once funk 
to the bottom, and did not rife when the air was exhaud- 
ed ; nor, when afterwards taken out, wiped dry, and 
laid on the floor of the receiver, did it exhibit any dwel¬ 
ling under the exhaultion of the veflel. The experiment 
was repeated with a fimilar refult on a portion of the 
vena cava of a pig. (Phil. Tranf. lxiv. 345.) 
Neither do the effedts refulting from the admixture of 
aeriform fluids with the blood, favour the notion of the 
entrance of air into that fluid. “ Animal, cui aer in fan- 
guinem inflatur,” fays Haller, “ perit certo et velociter; 
neque quidquam fatis certi ed in fanguinis venarum pul- 
monalium audio rubore.” (Loc. cit.) This affertion is 
confirmed likewife by diredt experiment. When Dr. 
Girtanner injedted oxygen gas into the jugular vein of a 
dog, he cried dreadfully, breathed quick, and died in 
three minutes: when nitrogen gas was thrown in, death 
happened in 20 feconds. (Memoirs on Irritability, pp. 
sat. 223.) Air, lays Bichat, thrown into the vafcular 
fydem, quickly brings on agitation, convulfions, and 
death. (Recherches fur la Vie et la Mort, p.179.) By 
forcing air through the windpipe into the lungs with a 
fyringe, and confining it there, he has made it to enter 
into the blood-veffels, which immediately brings on 
agitation, and exertion in the animal ; and, if an artery in 
the leg or foot be now opened, the blood will fpring out 
frothy, and full of bubbles of air. If hydrogen gas has 
been ufed, the bubbles may be inflamed ; and, when this 
frothy blood has flowed 30 feconds, the adtions of life 
ceafe, and cannot again be reftored, even although frefli 
air be fupplied. (Ibid. 303. Inquiry, § 102, 103.) 
If, then, no proof exilt of the pafi’age of air into the 
blood by the ordinary courfe of the abforbent veffels, 
the only other mode of effedting this purpofe that has 
been hitherto fuggelted, is the power of chemical affinity. 
What then are the chemical affinities fubfifting between 
venal blood and atmofpheric air? About the middle of 
the 17th century, Dr. Lower obferved, that the upper 
furface of venal blood, received into a veflel, acquired a 
fcarlet colour by expofure to the air; that, if this furface 
was removed, thefubjacent one yfas foon changed to the 
fame colour; that, if the cake of blood, after being al¬ 
lowed to fettle in the veflel, was inverted, its exterior 
and upper furface fpeedilyalfo affumed a florid hue; and, 
laftly, that if venal blood was ffiaken in a veflel, fo that 
the air thoroughly intermixed with it, it became entirely 
florid. (De Corde, p. 178.) Thefe opinions were after¬ 
wards held by Sig. Fracaffati and Dr. Slare, the latter of 
whom obferves, that the blood thrown up by a rupture of 
the capillary vefl’els of the lungs, is frothy, and of a fcar¬ 
let colour ; the firll of which effedls he attributes to the 
intermixture of air, and the latter to its tinging power. 
(Lowthorp’s Abridg. Phil. Tranf. iii. 235.) Mr. Hewlon 
employed fimilar arguments to prove, that the florid co¬ 
lour, acquired by venal blood on expofure, was produced 
by the contadl of the air; and, by injedting air into the 
jugular vein of a rabbit, he found that it there alfo ren¬ 
dered the blood florid. (Hewfon on the Blood, p. 9.) 
M. Cigna not only confirmed the foregoing fafis, but 
proved alfo that the change of colour in this fluid did not 
take place when the blood was covered with oil, or placed 
in vacuo ; and Dr. Prieftley afcertained, that not only by 
common air, but more efpecially by oxygen gas, this flo¬ 
rid colour was produced on the black craflamentum of 
blood. (On Air, iii. 66.) 
In effecting thefe remarkable alterations in the colour 
of the blood, the air itfeif, at the fame time, fufters ma¬ 
terial changes. Dr. Prieftley found, that in twenty-four 
hours oxygen gas was fo far depraved by being in contact 
with venal blood, that one meafure of it and two ot ni¬ 
trous gas occupied the fpace of a meafure and a half, 
whereas, at the beginning of the experiment, they occu¬ 
pied the fpace of no more than half a meafure. (Loc. cit. 
p. 75.) Dr. Goodwyn confined venal blood under ajar 
of oxygen gas inverted in mercury, and repeatedly ob¬ 
ferved that the change of colour was always very fudden, 
and, after feveral minutes, the mercury afcended two or 
three lines; from which he concluded that a fmall por¬ 
tion of the air had difappeared. (Effay, p. 61.) The pre- 
cife change, however, which the air underwent, feems 
firft to have been obferved by Dr. Girtanner, who placed 
fix ounces of venal blood in a jar ot oxygen gas inverted 
in mercury; the blood prefently affumed a florid colour; 
the air was fornewhat diminifhed in bulk, and contained 
a portion of carbonic acid, which was attradled by lime- 
water. (Beddoes’s Obf. on Calculus, &c. p. 219.) Dr. 
Bollock obferves alfo, that a diminution ot oxygen and 
production of carbonic acid take place when a'piece of 
craflamentum is placed in a jar filled with oxygen gas. 
(On Refpiration, p. 227.) The fame production of car¬ 
bonic acid occurs when blood is placed in contadl: with 
atmofpheric air. A quantity of this fluid was.received 
into a cup, and confined in a jar of air inverted in water, 
a glafs of lime-water having been previoufly placed in the 
cup. 
