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OBSERVATIONS

O N

RESPIRATION,

AND THE USE OF

THE B L O O D.

BY JOSEPH PRIESTLEY, LL.D, F.R.S.

Head at the R O Y A L SOCIETY, Jam 25, *77<S.

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LONDON:

Printed in the Year MDCCLXXVI.

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OBSERVATIONS, &c.

THERE is, perhaps, no fubjeil in phyilology, and very few in philofophy in general, that has en- gaged more attention than that of the ufe of refpiration. It is evident, that without breathing moft animals would prefently die ; and it is alfo well known, that the fame air will not long anfwer the purpofe : for if it has been fre- quently refpired, the breathing of it is as fatal as the total deprivation of air. But by what property it is, that air contributes to the fupport of animal life; and why air that has been much breathed will no more anfwer the purpofe, feems not to have been difcovered by any of the many philofophers and phyficians who have pro- feffedly written upon the fubje6t ; and it might have con- tinued to elude all direEl inveftigation, when it difcovered itfelf, without any trouble or thought, in the courfe of my refearches into the properties of different kinds of air, which had at firft quite another objeit.

In thefe experiments it clearly appeared, that refpiration isixpblogijtic procefs, affedting air in the very fame manner

A 2 as

4 Dr. Priestley's Obfervations on

as every other phlogiftic procefs (viz. putrefaction, the effervefcence of iron-filings and brimftone, or the calcina- tion of metal s,&c.) affe&s it ; diminifhing the quantity of it in a certain proportion, leflening its fpecific gravity, and rendering it unfit for refpiration or inflammation, bvit leaving it in a ftate capable of being reftored to a tolerable degree of purity by agitation in water, &x. Having dis- covered this, I concluded, as maybe feen Phil. Tranf. vol. LXII. p. 1 8 7 . and Obfervations upon Air^ vol. I. p. 7 8 . 2 7 7 . that the ufe of the lungs is to carry off a putrid effluvium^. or to difcharge that phlogifton, which had been taken into the fyftem with the aliment, and was become, as it were, effete ; the air that is refpired ferving as -zmenjlruum for that purpofe.

What I th en concluded to be the ufe of refpiration in ge- neral, I have now, I think, proved to be effected by means of the bloody in confequence of its coming fo nearly into contact with the air in the lungs ; the blood appearing to be a fluid wonderfully formed to imbibe, and part with, that principle which the chemifts call phlogifton, and changing its colour in confequence of being charged with it, or being freed from it ; and affecting air in the very fame manner, both out of the body and in the lungs ; and even notwithftanding the interpofition of various fub- ftances, which prevent its coming into immediate con- tail with the air.

As it may not be unpleafing or unufeful, I fhall, before I relate my own experiments, briefly recite the principal of the opinions which have been held con- cerning

Refpiration, and the Ufe of the Blood.. 5;

eerning the ufe of refpiration, from haller's excellent Syjiem of Phyjiology, and fome others of the molt eminent writers upon that fubjedt.

Hippocrates reckoned air among the aliments of the body. But it was more generally the opinion of the an- cients, that, there being a kind of vital fire kept up in the heart, the heat of the blood was tempered in the lungs. galen alfo fuppofes, that there was fomething equiva- lent to a fire conftantly kept up in the heart; and that the chief ufe of the lungs was to carry off fuch vapours as were equivalent to fmoke thrown off from that fire.. haller, vol. III. p. 354. cartesius maintained the fame vital fire in the heart, fuppoling that air was ne— ceffary for cooling and condenfing the blood. Ibid. p. 343..

Of the more modern phyfiologifts, fome have thought; that the air itfelf is taken into the lungs ; others, that it is only fomething extracted from the air, as the more fubtle parts of that fluid, an ether, or aerial nitre; while others fuppofe it to be the air itfelf, but diffolved in water, and therefore in an unelaftic flate, ibid. p. 3 2 1 .

Moft of thofe who think that air is taken into the blood fuppofe it to be taken in by the lungs, ibid. p„. 330. Some fuppofe, that the effect of the admiffion of this air into the blood is a fermentation, p. 332. Others fuppofe, that it aits by its fpring, preventing the too clofe contadt of the globules, and thereby pre- ferring its fluidity, inteftine motion, and heat, ibid, ber- tier fuppofed, that the circulation of the blood was, in a great meafure, owing to the admiffion of air into it. van helmont afcribed the volatility of. the fixed ele- ments

6 Dr. Priestley's Obfervations on

merits in the food to this air, p. 336.; and stevenson thought, that the air which had circulated in the blood, and which had heated the blood too much, was exhaled by the lungs, p. 355.

Others fay, that the air itfelf is not admitted into the hlood, but only fome adtive, fpirituous, and ethereal par- ticles ; that this vital fpirit paffes from the lungs to the heart and arteries, and at length becomes the animal fpi- xits, which are by this means generated from the air, p. 333. Others, who do not admit that the animal fpirits are derived from the air, flill fay that fome other vital principle comes from thence. This vital principle mal- pighius fuppofes to be a faline vapour; lister, a hot, inflammable, fulphureous fpirit; vieussenius, a volatile acid fait, which keeps up the fermentation of the blood ; and bryan robinson, the aerial acid, which preferves the blood from putrefadtion; preferves alfo its denfity, and ftrengthens the animal fibres. For this reafon he fup- pofes it is that we feel ourfelves refrefhed in cold air, as it abounds with a more plentiful acid quality, p. 334- They who fuppofe that nitre is taken from the air into the blood, afcribe to that principle its fermentation, its heat, and its denfity, p. 334.

It is a received opinion, that one ufe of the lungs is to attenuate the blood, p. 359; and malpighius adds, that by this means, the different particles of the blood become thoroughly mixed together; while others think that the blood is condenfed in the lungs ; and others, that the globules, and all the finer humours, receive their con- figuration there, ibid. Some, without confidering the

air

Refpiration, and the UJe of the Blood. ?

air as of any other ufe than to put the lungs in motion, think, that heat is produced in the lungs by the attrition, of the blood in paffing through them .Mifc. Taurin. voL V. p. 36. The red colour of the blood has been thought by fome to be caufed by this attrition in the lungs; but lower refuted this notion, chiefly by obferving, that the attrition of the blood is greater in the mufcles, from which, however, it always returns black, Ibid. vol. I. p. 7 4- Dr. why tt thought there was fomething of a vital, and ftimulating nature derived from the air into the blood, by means of which it made the heart to contract,

HALLER, VOl. III. p. 336.

boerhaave fays, that air not changed is deadly; not on account of heat, rarefaction, or denfity, but for fome other occult caufe. Mifc. Taurin. vol. V. p. 30.

Dr. hales, who has thrown much more light upon the dodtrine of air than all his predeceflbrs, was equally ignorant of the ufe of it in refpiration; and at different times feems to have adopted different opinions concern- ing it.

In his Statical Effays, vol. II. p. 3 2 1 . he fuppofes, that air is rendered alcaline by breathing, and corrected, in fome meafure, by the fumes of vinegar.

In agreement, as he obferves, with boerhaave, he fays, p. 100. that the blood acquires its warmth chiefly in the lungs, where it moves with much greater rapidity than in, any other capillary vefTels of the body, vol. II. p. 87; hut that one rife of the air is to cool the blood, p. 94 ; and he makes an eftimate of the degree of this refrigeration. The red colour of the globules of blood, he fays, p. 88,

intimates

8 T)r. priestley's Obfervations on

intimates their abounding with fulphur, which makes them more fufceptible and retentive of heat than thofe bodies which have lefs of it.

He alfo fuppofes, p. 102, that another great ufe of the lungs is to attenuate and feparate the globules of blood; and that the floridnefs of the arterial blood above the ve- nal may, in a good meafure, be owing to the ftrong agita- tion, fri6tion, and comminution, which it undergoes in palling through them. In like manner, in an experiment which he made for the purpofe, blood much agitated in a clofe glafs veffel was obferved to be very florid, not only on its iurface, but through its whole fubftance, as arterial blood is, vol. II. p. 1 o 2. I would obferve, however, that in this expement, the blood muft have acquired its florid colour from the air with which it was agitated*

He adds, that it is probable, that the blood may, in the lungs, receive fome other important influence from the air, which is in fuch great quantities infpired into them. In other places, however, he explodes the dodlrine of a vivifying fpirit in the air. It has long, he fays, been the fubjeft of inquiry to many, to find of what ufe it is in refpiration ; which, though it may in fome refpe<5ts be known, yet it muft be confeffed, that wTe are ftill much in the dark about it, vol. II. p. 102.

Suffocation, he fays, vol. II. p. 27 1 > confifts chiefly in the falling flat of the lungs, occafioned by the groflhefs of the particles of a thick noxious air, they being, in that floating ftate, moft eafily attracted by each other, as we find that fulphur, and the elaftic repelling particles of air are ;

and

Refpiration, and the Ufe of the Blood. 9

and confequently unelaftic, fulphureous, faline, and other floating particles, will moft eafily coalefce, whereby they are rendered too grofs to enter the minute veficles, which are alio much contracted, as well by the lofs of the elafti- city of the confined air, as by the contraction occafionedby the Simulating acid fulphureous vapours. And hence it is not improbable, that one great defign of nature in the ftruCture of this important and wonderful vifcus^ was to frame the veficles fo very minute} thereby effectually to hinder the ingrefs of grofs, feculent particles, which might be injurious to the animal economy.

Laftly, he concludes, that the effeCt of refpiration is to abate, and in part deftroy, the elafticity of the air; and as this was effected by fuphureous vapours, and he could breathe for a longer time air that had pafled through cloaths dipped in a folution of fait of tartar, he con- cluded, that the air had been mended by the tartar hav- ing ftrongly imbibed the fulphureous, acid, and wratery vapours, voL I. p. 267.

haller, after reciting the opinions of all that had gone before him, fuppofes, with Dr. hales, that, in con- lequence of the air lofing its fpring in the lungs, they cannot be kept dilated; and therefore, they muftcollapfe, and the circulation of the blood be impeded, vol. III. p. 258. When he ftates his opinion concerning the ufe of the lungs more fully, he fays, that the true ufe of them is partly inhaling, and partly exhaling, p. 351. That the lungs inhale both water and air; but that in the lungs the air lofes its elaftic property, lb as to be eafily foluble in water or vapour, p. 352,: and he thinks it

B probable,

io Dr. priestley's Obfervations on

probable, that this air ferves as a cement to bind the earthy parts together. He alfo makes no doubt, but that various other matters, mifcible with water, are inhaled by the lungs ; and he even thinks it not improbable, that the air may carry fome eleitric virtue along with it. The principal exhalation of the lungs, he thinks, to be water, abounding with oily, volatile, and faline principles ; and thefe oily and fetid vapours, he thinks, to be the fuligines of galen and other ancients, p. 354.

Mr. cigna of Turin, has given much attention to this curious fubjeft, as appears by two Memoirs of his; one in the firft volume of the Mifcellanea 'Taurinenfia, in which he very well accounts for the florid red colour of the blood; and the other, which is a much more elaborate Memoir, intitled, DeRefpiratione> in the fifth volume of the fame work, juft publifhed, or about to be publifhed, the copy of the article having been fent to me by the author.

He takes it for granted, that air which has once been breathed is unfit for farther refpiration, on no other ac- count than its being loaded with noxious vapours, which difcover themfelves by a fetid fmell. Mifc. Tattrin. vol. V. p. 30. And he takes it for granted, that the elafticity of air is diminiihed by refpiration, though he does not confider that diminution of elafticity as the caufe of its noxious quality. He therefore concludes, that air which has been breathed, fuffocates by means of the irritation which it occafions to the lungs, by which the bronchia, and the lungs themfelves, are contracted, fo as to refift the entrance of the air* and therefore, that refpired air is,

noxious

Refpiration, and the Ufe of the Blood. 1 1

noxious on the fame account as mephitic vapours, or thofe of burning brimftone, p. 3 1 ; that, in frequently breath- ing the fame air, it becomes fo loaded with thefe vapours, as to excite a convulfion in the lungs, and thereby render them unfit for tranfmitting the blood, p. 42.

This philofopher fuppofes that air enters the pores of the blood, retaining its el aftic power, p. 50. and that it continues at reft there, becaufe its endeavour to efcape is counteracted by the equal preffure of the ambient me- dium, p. 52. This air, he fuppofes to be introduced into the blood by the chyle, and never by the way of the lungs, except when, by fome means or other, the equili- brium between the air in the blood and the external air is loft, p. 57. If the external air be rarer than the inter- nal, the air in the blood, expanding itfelf, will inflate the animal, and have the fame effeit as air introduced into the veins.

What we are chiefly indebted to M. cigna for, is his decifive experiments with refpecSt to the florid colour of the blood, which he clearly proves to be caufed by the contacSt of air; though he afterwards feems willing to de- fert that hypothefis. It was often imagined, that the reafon why the lower part of a quantity of blood was black, while the furface was red, was, that the black par- ticles, being heavier than the reft, fubfided to the bot- tom; but this opinion our author clearly refutes.. He found, that when he put a little oil upon a quantity of blood, it remained black throughout ; but that when he took away the red part, and expofed to the air the lower

B 2 lamina.

12 Dr. Priestley's Obfervations on

lamina, which were black, they alfo became fucceffively red, till the whole mafs acquired that colour, Mifc. Tail- rin. vol. L p. 73. Alio, at the requeft of M. cigna, Fa- ther beccaria tried what would be the effect of expofing blood in vacuo; and he found, that in thofe circum- ftances, it always continued black; but that, by expofing it again to the air, it became red, p. 68.

M. cigna concludes his firft differtation with obferving, that it is not eafy to fay how it comes topafs,that the lower part of a mafs of blood becomes black, whether by the air which it had imbibed efcaping from it, or by its depofit- ing fomething faline, neceffary to contribute to its red- nefs, or by the preffure of the atmofphere ; but he in- clines to think, that air mixed with blood, and interpofed between the globules, preferves its rednefs : but that by concreting it is expelled from it, or becomes fo fixed as to be incapable of making it red. This opinion, he thinks, is rendered in fome meafure probable, by the in- creafed denfity of concreted blood, and by the emiffion of air from other fluids in a concrefcent ftate, p. 74.

Notwithftanding what he had advanced in his firft Memoir, yet inthefecond, which was written feveral years after it, he doubts whether the change of colour in the blood takes place in the lungs ; but if it does, he inclines to afcribe this effed: to the evaporation from the blood in the lungs : and though he always found, that the co- lour of the blood was changed by the contact of air, yet when he confidered that evaporation muft, as he thought, nectffarily attend the contact of air, he imagined, that this

effeft:

Refpiration, and the Ufe of the Blood. 1 3

effeft might equally be attributed to this circumftancc. gut he acknowledges, that this hypothefis ought not to be received till it be confirmed by experiments, Mifc. 'Taurin. vol. V. p. 61.

Upon the whole, he concludes, that the principal ufe of air to the blood, is to preferve the equilibrium with the ex- ternal air, and to prevent the veffels from being rendered unfit to tranfmit the blood, on account of the external preffure; whereas, by means of the air they contain, the fluids move in their proper veffels as freely as in vacuo, and the membranes and vifcera alfo eafily Hide over each other, p. 63. And with refpe6t to the ufe of the lungs, fince he imagined that air is not introduced into the blood by means of them, he thinks, that becaufe fuch lungs as thofe of man are given to the warmer animals only, the chief ufe of refpiration is exhalation, and confequently the cooling of the blood, p. 65.

The laft wrriter whom I fhall quote upon this fubje£ty is the late ingenious Mr. hewson; who fays, in his Ex- perimental Inquiry into the Properties of Blood, p. g. " As the colour of the blood is changed by air out of the " body, it is prefumed, that the air in the lungs is the " immediate caufe of the fame change in the body." That this change is really produced in the lungs, he is perfuaded, he fays, from experiments, in which he dif- tin6lly faw the blood of a more florid red in the left au- ricle of the heart than it was in the right ; but how this; effeft is produced, he fays, is not yet determined.

Since

14 Dr. Priestley's Obfervations on

Since fome of the neutral falts, and particularly nitre, has a fimilar effedt on the colour of the blood; fome, fays he, attribute this difference to the nitre ab- forbed from the air, while in the lungs. But this, he adds, is a mere hypothefis> for air contains no nitre, and moil of the neutral falts produce the fame effedt in fome degree.

Since, however, a folution of nitre does produce this effect upon blood, inftantly making the very blacked of it of a beautiful florid red, though this effect is not pe- culiar to nitre (for a folution of common fait does nearly the fame thing) I own I am inclined to afcribe this effect to the air; efpecially fince 1 have proved, as I apprehend, that atmofpherical air confifts of earth and fpirit of nitre. Poffibly, therefore, the air we breathe may be fo far de- compofed, as to communicate fomething of nitre to the blood, in its pafTage through the lungs.

After this review of the obfervations and opinions of others on this important queftion in phyfiology, I fhali proceed to recite my own. It may appear fomething. ex- traordinary, that among fuch a variety of opinions concern- ing the ufe of refpiration, the right one fhould never have been fo much as conje£tured, though unfupported by the proper proof. But indeed, this animal function, and the phlogiftic proceffes in chemiftry, efpecially that of the calcination of metals, which is, perhaps, the moft fimple of them, are to appearance very different things ; and therefore, it is the lefs to be wondered, that no perfon

fhould

Refpiration, and the life of the Blood. 1 5

ihould have imagined, they would produce the fame effect on the air in which they were performed.

That refpiration, however, is, in reality, a true phlogiftic procefs, cannot, 1 think, admit of a doubt, after its being found, that the air which has ferved for this purpofe is left in precifely the fame ftate as that which has been ex- pofed to any other phlogiftic procefs. And fince all the blood in the body paffes through the lungs, and, accord- ing to Mr. hewson's obfervations and others, the re- markable change between the colour of the venal and arterial blood takes place there, it can hardly be doubted, that it is by means of the blood that the air becomes phlogiiticated in paffing through the lungs; and there- fore, that one great ufe of the blood muft be to difcharge the phlogiflon with which the animal fyftem abounds,, imbibing it in the courfe of its circulation, and imparting it to the air, with which it is nearly brought into contact , in the lungs ; the air thus adting as the great menftruum for this purpofe.

Though J had no doubt concerning this conclufioat from my former experiments, I thought fo great a pro- blem deferved as much ilhiftration as could be given to it ; and therefore I was willing to try, whether the blood was of fuch a nature, as to retain any of this power of affedt- ing air when congealed, and out of the body, that it has when it is fluid, and in the body ; and the experiments have fully anfwered my expectations.

Having taken the blood of a flieep, and let it ftand till it was coagulated, and the ferum was feparated from it (after which the furface, being expofed to the common

air*

1 6 Dr. Priestley's Obfervations on

air, is well known to aflume a florid red colour, while the infide is of a much darker red, bordering upon black) I introduced pieces of the craflamentum, contained in nets of open gauze, or of wire, fometimes through water, and ibmetimes through quickiilver, into different kinds of air, and always found that the blackeft parts affumed a florid red colour in common air, and more efpecially in de- phlogifticated air, which is purer and more fit for refpi- ration than common air (and accordingly the blood al- ways acquired a more florid colour, and the change was produced in lefs time in this than in common air) whereas the brighteft red blood became prefently black in any kind of air that was unfit for relpiration, as in fixed air, inflammable air, nitrous air, or phlogifticated air; and after becoming black in the laft of thefe kinds of air, it regained its red colour upon being again expofed to com- mon air, or dephlogifticated air ; the fame pieces becom- ing alternately black and red, by being transferred from phlogifticated to dephlogifticated air ; and vice verfa.

In thefe experiments the blood muft have parted with its phlogifton to the common air, or dephlogifticated air, and have imbibed it, and have become faturated with it, when expofed to phlogifticated, nitrous, inflammable, or fixed air. The only difficulty is with refpecl to the fixed air; for all the other kinds certainly contain phlogifton. But, as I have obferved in the account of my experi- ments on vitriolic acid air, phlogifton feems to be necef- fary to the conftitution of every kind of air; and befides, the blacknefs of the blood may arile from other caufes

than

Refpiration, and the Ufe of the Blood. 1 7

than its acquiring phlogifton. gaber, for inftance, ob- ferves, that blood becomes black when it begins to pu- trify, as it does alfo whenever it is dried and hardened near the fire. Father beccari a alfo found, as I have ob- ferved, that red blood continued (and he could hardly fail to obferve alio, that it became) black in vacuo, where it could not have imbibed phlogifton. This I found to be the cafe when the blood was covered two inches and a half with ferum ; but it regained its florid colour when it was expofed to the open air.

A In general, however, it cannot be expelled, that when blood has become black without having received phlo- gifton ab extra, it will recover its florid colour by being expofed to the air. For the delicacy of its texture, and confequently its capacity of being eafily affeited by phlo- gifton, may be effentially altered by internal caufes of blacknefs. This is even the cafe when blood has become black by being expofed to nitrous and inflammable air, though this change is probably effedted by its imbibing phlogifton.

I expofed pieces of the fame mafs of red blood to thefe two kinds of air, and alfo to fixed air at the fame time. They all became black ; but that which was in the in- flammable air was the leaft fo, and none of them reco- vered their florid colour in the open air. But at another time, a piece of craflamentum, which had become black in fixed air, did, in fome meafure, and very flowly, reco- ver its florid colour in dephlogifticated air. Perhaps the pieces that had loft their colour in the nitrous and

C inflam*

1 8 Dr. Priestley's Obferv.

inflammable air might have recovered it by means of this more powerful menftruum.

Since, however, blood, after becoming black in phlo- gifticated air, is always capable of reluming its red co- lour on being again expofed to pure air, it may be con- cluded, that the preceding blacknefs, difcharged in the pure air, and producing the conftant effeit of phlogifton, ing the air, was owing to the phlogifton it had imbibed in the former fituation, and which it parted with in the latter. And this is remarkably the cafe when blood is transferred from phlogifticated into dephlogifti- cated air. Even the circurnftance of the deeper colour is fufficient to give a chemift a fufpicion that it contains more phlogifton than blood of a lighter colour.

When I had found how readily pieces of blood changed their colour, according to the quality of the air to which they were expofed, I proceeded to examine the ftate of that air, in order to obferve what change had taken place in it; and as dephlogifticated air admits of a more fenfi- ble change of quality than common air, I gave it the pre- ference in this experiment; putting a piece of crafla- mentum, about the bignefs of a walnut, into the quantity of about five ounce meafures of this air.

This procefs I continued for the fpace of twenty-four hours, changing the blood about ten or twelve times; after which I found the air fo far depraved, that whereas, at the beginning of the experiment, one meafure of it and two of nitrous air occupied the fpace of no more than half a meafure, the fame mixtures afterwards occupied

the

Refpiration, and the Ufe of the Blood. 1 9

the fpace of a meafure and a half. Now fince air is uni- verfally depraved by phlogifton, and in this fenfe, I be- lieve, by nothing elfe, it is evident, that this black blood mult have communicated phlogifton to the air; and con- fequently its change of colour from black to a florid red muflr have been occafioned by the reparation of phlo- gifton from it.

The next day, when, of courfe, the blood was nearer to a ftate of putrefadlion, in which every kind of iub- ftance, without exception, will injure refpir able air, I put a quantity of red blood, tinged in a few places with black, which I could not eafily feparate from it, to about the fame quantity of the fame dephlogifticated air, and fufFered it to ftand, without changing, for the 'fame fpace of time; when it was fo little injured, that the meafures abovemen- tioned occupied the fpace of only two-thirds of a meafure.

That blood has a power of taking phlogifton from air, as well as imparting phlogifton to air, I fatisfied my- felf by expoiing blood of a very beautiful florid colour to nitrous air, inflammable air, and phlogifticated air. The two firft mentioned kinds of air were coniiderably diminifhed by the procefs, which was continued two days, during which time the blood had been changed five or fix times.

The nitrous air, by this means, loft a great proportion of its power of diminifhing, that is, phlogifticating, common air. For now two meafures of common air and one of this occupied the fpace of 2^, inftead of i| mea- fures. The inflammable air, though ftill inflammable,

C 2 was

20 Dr. priestley's Obfervations on

was rendered in fome degree wholefome by the procefs ; being, after this, confiderably diminished by nitrous air, which is a ftate to which it is brought by agitation in water, and which, continued longer, deprives it of its in- flammability likewife. It cannot be doubted, therefore, but that, in both thefe cafes, the red blood, by becoming black, received phlogifton from thefe two kinds of air.

ith refpect to the phlogifticated air, I only obferved that, after a few hours expofure to the red blood, it was f enfibly, but not much, diminifhed by nitrous air, which otherwife it would not have been in the leaft degree. This blood, however, was of the light eft colour; that is, according to my hypothefis, the moft free from phlo- gifton, of any that I have ever feen ; and I have tried the fame thing, without fuccefs, with blood of a lefs florid colour, though as florid as the common air could make it. But it fhould be confidered, that the proper function of the blood is not to receive phlogifton from #/>, not meeting with any phlogifticated air in the courfe of its circula- tion, but to communicate phlogifton to air; and there- fore, there is by no means the fame reafon to expeit, that air will be mended by red blood, as that it will be injured by black blood.

It may be objedted to this hypothefis, concerning the ufe of the blood, that it never comes into actual conta6t with the air in the lungs, but is feparated from it, though as Dr. hales ftates it, at the diftance of no more than a thoufandth part of an inch. The red globules alfo fwim

in

Refpirailon, and the Ufe of the Blood. % i

in a large quantity of ferum, which is a fluid of a quite different nature.

In order to afcertain the effe£l of thefe circumftances, I took a large quantity of black blood, and put it into a .bladder moiftened with a little ferum, and tying it very clofe, hung it in a free expofure to the air, though in a quiefcent itate ; and the next day I found, upon exami- nation, that all the lower furface of the blood, which had been feparated from the common air by the intervention of the bladder (which is an animal membrane, fimilar to that which conftitutes the veficles of the lungs, and is at leaft as thick) and likewife a little ferum, had acquired a coating of a florid red colour, and as thick, I believe, as it would have acquired, if it had been immediately ex- pofed to the open air ; fo that this membrane had been no impediment to the adtion of the air upon the blood. In this cafe it is evident to obferve, that the change of co- lour could not be owing to evaporation, as Mr. cign a con- jectures. This experiment I repeated, without previoufly moiftening the bladder, and with the very fame refult.

I obferved alfo, that when I cut out a piece of the craffamentum, and left the remainder in the veffel writh the ferum, not only that part of the furface which was expofed to the air, but that which was furrounded with ferum, and even covered with it to the depth of fe- veral inches, acquired the florid colour; fo that this deep covering of ferum, which muft have effectually prevented all evaporation, was no more an impediment to the mu- tual action of the blood and the air, than the bladder had

been.

22 Dr. priestley's Obfervations on

been. The ferum of the blood, therefore, appears to be as wonderfully adapted to anfwer its purpofe, of a vehicle for the red globules, as the red globules themfelves : for the flighted covering of water, or faliva, effectually pre- vents the blood from acquiring its florid colour; and Mr. cigna found that this was the cafe when it was covered with oil.

That it is really the air, a6ting through the ferum, and not the ferum itfelf, that gives the florid colour to the blood, is clearly afcertained by the following experiment. I took two equal portions of black blood, and put them into equal cups, containing equal quantities of ferum, which covered them to the depth of half an inch. One of thefe cups Handing in the open air, and the other being placed under an exhaufted receiver, the former prefently acquired a florid colour, while the other continued twelve hours as black as at firft. Being taken out of the receiver, it flood all night in the open air without becoming red, and continued black ever after, even when the ferum was poured off.

I alio more completely fatisfied myfelf of the influence of the air upon the blood, through a body of ferum, by the reverfe of this experiment. For I found that red blocd became black through the depth of two inches of ferum, when the veflel containing it was expofed to phlogifticated air; fo that the red globules of the blood both receive, and part with phlogifton by means of the air, notwithftanding the interpofition of a large body of the fluid in which they naturally float.

Except

Refpiratmiy and the Ufe of the Blood. 1 3

Except ferum, milk is the only animal fluid that I have tried/ through which the air can act upon blood: for black blood became red when it was plunged in milk, in the fame manner as if it had been covered with ferum. In urine, indeed, black blood becomes inftantly red; but this is not owing to the adtion of the air, through the urine, but to the faline nature of that fluid.

In fome cafes, care rauft be taken to diftinguifh the floridnefs with which fome detached parts of a quantity of blood are tinged, from that which penetrates the folid parts of it. In faliva^ and in water impregnated with alkaline fait, fixed or volatile, and alfo in fpirit of wine, the extreme angles and edges of pieces of craflamentum and fmall detached parts, floating in thofe liquors, will appear of a very florid red, while the compact mafs of blood continues dark. The florid colour of the promi- nent and detached parts, in thefe cafes, feems to be the mere effect of the minute diviiion of the parts of the craflamentum in the fluid in which thofe parts float; when at the fame time it has no fuch effedt on thofe parts which remain compact, nor has the air the leaft -power of adting on the blood through the liquor.

I had imagined, that iince black blood contains more phlogifton than red blood, that difference would have appeared in the air produced from them, either by being Amply diflblved in fpirit of nitre, or when dried and made into a pafte with that acid. But the difference wras too fmall to be fenfible to this kind of telt. For this purpofe, however, I had fome blood drawn from the vein

of

1 4 Dr. Priestley's Observations on

of a fheep, and alfo took fome that came firft after killing it, as the butchers ufually do, by dividing the carotid ar- tery ; but though I diffolved the black part of the for- mer, and the red part of the latter, in equal -quantities of the fame fpirit of nitre, I found ho fenfible difference in the air that they yielded. The air that I got from them when dried, and made into a pafte with fpirit of nitre, was likewife equally indiftinguifhable. The quantity of air from this procefs was very great, and was produced irregularly, as I have obferved it to have been when pro- duced by a folution in fpirit of nitre without drying. Obfervations on Airy vol. II. p. 155. Half of this pro- duce was fixed air, and the reft phlogifticated, except that a candle burned in it with a lambent blue flame. It is evident, however, from this experiment, that even the moft florid blood contains a confiderable quantity of phlogifton; for, other wife, this air would have been de- phlogifticated*

I would conclude this paper with obferving, that I have found a very great difference in the conftitution of blood with refpedt to its property of being affeited by the influence of the air; fome becoming very foon of a light florid colour, and the Jlratum of this colour foon grow- ing very thick; whereas, in other cafes," the colour of the blood, in the moft favourable circumftances, has con- tinued much darker, and the lighter colour has never penetrated very f ar/ ^^^

As the principal ufe of the blood feems to be its power

<of receiving and difcharging phlogifton, and the degree jNDED 1 Wrz .

cheading:3 Respiration . and the Use of the Blood.

in which it possesses this power is easily ascertained by the eye, it might not, perhaps, be unworthy of being par- ticularly attended to by physicians. To estimate the goodness of blood, according to this criterion, nothing is requisite but to observe the lightness of the colour, and the depth of the 1 Irjht- coloured stratum, after it Las been exposed to the air for a given time. In cases in which the blood is unusually black, and but little affected by common air, it should seem, that breathing a purer air might be prescribed with advantage.

In general, the Blood that I have been able to procure in the city has not been so good as that which I have got in the country; owing, perhaps, to the cattle having been much driven, and heated before they were killed .

cEnds here in middle of p. 25. Transcribed, 1941, from the Osier Library copy of Priestley's "Observations on Respiration ...", 1776. 3