RESPIRATION. 



«-yn confined venal blood under a jar of oxygen gas inverted 

 in mercury, and repeatedly obferved that the change of co- 

 lour was always very fudden, and, after feveral minutes, the 

 mercury afcended two or three lines ; from which he con- 

 cluded that a fmall portion of the air had difappeared. 

 (Effay, p. 61.) The precife change, however, which the 

 air underwent, feems firft to have been obferved by Dr. 

 Girtanner, who placed fix ounces of venal blood in ajar of 

 oxygen gas inverted in mercury ; the blood prefently af- 

 fumed a florid colour ; the air was fomewhat diminiihed in 

 bulk, and contained a portion of carbonic acid, which was 

 attracted by lime-water. (Beddoes' Obf. on Calculus, &c. 

 p. 219.) Dr. Boftock obferves alfo, that a diminution of 

 oxygen and production of carbonic acid take place when a 

 piece of craffamentum is placed in a jar filled with oxygen 

 gas. (On Refpiration, p. 227.) The fame production of 

 carbonic acid occurs when blood is placed in contact witli 

 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. 

 The internal furface of the jar was foon bedewed with 

 moiiture, and a pellicle began to form on the lime-water, 

 which, in a few hours, was increafed to a thick cruft of car- 

 bonate of lime. The craffamentum was then removed, and 

 a frefli glafs of lime-water was placed in the ferum, which, 

 in thirty-fix hours, had acquired a cruft like the former, 

 and the water had rifen coniiderably into the jar. In an- 

 other experiment, where the ferum was placed for twenty- 

 four hours in a jar of air inverted in mercury, the refidual 

 air rendered lime-water milky, and the remainder had loft a 

 part of its oxygen. A fimilar production of carbonic acid 

 feems to have oceurred, when, with a fmall diminution of 

 the gas, a flight change of colour was produced on venal 

 blood by placing it in contact with nitrous oxyd, in the 

 experiments of Mr. Davy ; for when a folution of ftrontian 

 was admitted to the oxyd, it became flightly clouded, and, 

 with the diminution of bulk that followed, minute portions of 

 carbonic acid and nitrogen gas were produced. (Refearches, 

 pp. 377. 380. 387.) Hence then we learn, that when venal 

 blood is expofed to the contact of atmofpheric air, of 

 oxygen gas, or of nitrous oxyd, it prefently affumes a 

 florid colour, and, at the fame time, the volume of air is 

 lomewhat diminifhed, and a portion of carbonic acid is 

 produced. 



Does then the carbonic acid, which is here met with, 

 proceed ready formed from the blood, or is it in part formed 

 by the decompolition of the air ? No one has yet proved 

 that any aeriform fluid, much lefs that carbonic acid, exifts 

 naturally in the blood ; and if this be true, no fuch aerial 

 acid can be expected to iflue from it. The carbonic acid 

 alfo, is not formed by blood when it is confined in nitrogen 

 gas ; neither does the colour of the blood, in that cafe, un- 

 dergo any fenfible change ; but this acid is formed by blood, 

 either in oxygen gas, in nitrous oxyd, or in atmofpheric 

 air, all of which are deteriorated thereby ; whence it 

 follows, that without the prefence of oxygen gas, the blood 

 is unable to form carbonic acid, and that this acid, there- 

 fore, is, in part, formed out of that gas. If the oxygen 

 gas that difappears do not contribute to form the carbonic 

 acid that is produced, in what other manner can its lofs be 

 accounted for ? or from what other fource than the oxygen 

 gas of the air, in contact with the blood, can that ingre- 

 dient of the acid be derived ? Thofe who fuppofe the car- 

 bonic acid to be furnifhed by the blood, independent of the 

 air employed, muft likewife fuppofe that the nitrogen gas 

 js furniihed by it alfo ; for the experiments of Mr. Davy 



teach us, that a portion of that gas, as well as of carbonic 

 acid, is always prefent when nitrous oxyd is decompofed, 

 which renders it probable that the fame thing likewife occurs 

 when air is changed by venal blood. But in what manner 

 the blood fhouid be able to furnifh nitrogen gas, it is not 

 eafy to conceive, fince no affinity exifts between that gas 

 and venal blood. (Davy's Refearches, p. 375. ) We infer, 

 therefore, from thefe facts, that atmofpheric air is decom- 

 pofed by being placed in contact with venal blood, its oxy- 

 genous portion being in part converted into carbonic acid, 

 and a quantity of its nitrogen being, in confequence, left 

 free. 



But, fuppofing the air to be thus decompofed by the 

 blood, it ftill remains a queftion, whether it has been firft 

 attrafted by that fluid, then decompofed, and afterwards 

 in part expelled ; or, whether the decompolition lias been 

 effected without fuch previous attraction and intermixture 

 of air. The only evidence of this fuppofed attraftion feems 

 to be the fmall diminution of bulk, which the air in all 

 cafes fuffers ; but this cannot be confidered as a proof of 

 the attraftion of the air ; for it is a neceffary confequence 

 of that converfion of oxygen gas into carbonic acid, which 

 has been fhewn to take place, when thefe fubftances are 

 brought into contaft. Even granting to the blood this 

 power of attracting air, or its oxygenous portion, it is not 

 eafy to conceive, why it Ihould fo readily lofe it, and ao-ain 

 give out this air in the form of carbonic acid. No change 

 of quality in the blood, nor any variation of temperature, 

 can have taken place fufficient to alter fo rapidly its affiuity 

 for thefe fubftances : and it cannot proceed from a want 

 of affinity between the blood and the carbonic acid that is 

 formed ; for that acid fuffers a greater diminution, either 

 than oxygen gas or atmofpheric air, by being placed in 

 contact with blood. We incline, therefore, to the opinion, 

 that neither the air nor its oxygen gas is attrafted by, and 

 diffufed through the blood, as happens with feveral gafes 

 when placed in contact with certain fluids : but that the 

 air is decompofed, and its oxygen gas changed into car- 

 bonic acid, without entering into the fubftance of that 

 fluid. 



But, for the formation of this acid, the blood muft 

 fupply carbon, fince no other fubftance was prefent from 

 which it could be derived : and it is well known alfo, that 

 carbon enters largely into the compofition of that fluid ; 

 and our experiments prove, that it exifts as well in the 

 ferous as in the more folid parts. By fome it may be ob- 

 jected, that becaufe carbonic acid is formed directly by the 

 combuftion of charcoal, it cannot be produced at fo low 

 a temperature as exifts in thefe experiments. To this we 

 can reply only by an appeal to the general facts exhibited 

 through the whole courfe of our enquiry, by which it ap- 

 pears, that both by the living funftions of vegetables and 

 animals, and by the decomposition of animal and vegetable 

 matter, this acid is in like manner formed at temperatures 

 equally low. Even thofe, who confider this acid to have 

 proceeded ready formed from the blood, cannot attribute 

 its produftion to the operation of heat ; for in the animal 



body, the temperatnre of the blood feldom exceeds ioo° 



a degree of heat incompetent to form carbonic acid by anv 

 procefs analogous to combuftion. The combination of 

 many bodies is, indeed, greatly accelerated by being ex- 

 pofed to very high temperatures ; but this furely does not 

 let afide the fact of their fpontaneous union at temperatures 

 much more low. From this review of the effeas, which 

 take place between the blood and air, we conclude, that 

 the chemical phenomena, which arife when the fubftances 

 9 are 



