RESPIRATION. 



3G5 



The presence of a larger quantity of free 

 oxygen gas in the arterial blood than what 

 is sufficient to form the carbonic acid gas 

 evolved at the lungs, amounting in some cases 

 to rather more than 10 per cent, of the vo- 

 lume of the blood in the experiments of 

 Magnus, naturally leads to the conclusion 

 that the greater part, at least, of the absorbed 

 oxygen is not chemically combined in the 

 arterial blood, and is simply held in solution 

 by it. We are not, however, quite prepared 

 to concur in the opinion of Magnus, that the 

 whole of the absorbed oxygen is held in solu- 

 tion in the arterial blood, and that an inter- 

 change between part of the free carbonic acid 

 of the venous blood, and part of the oxygen 

 of the atmospheric air, embraces the entire 

 changes in the blood as it passes from the 

 venous to the arterial condition : for, if the 

 opinion be correct that the elaboration of the 

 materials of the chyle into blood is completed 

 in the lungs, and that certain marked differ- 

 ences in the fibrin of the two kinds of blood, 

 noticed above, really exist, something more 

 than this is probably necessary. Though the 

 experiments of Marchand appear to prove 

 that the absorbed oxygen does not enter into 

 any chemical combination with the consti- 

 tuent parts of the arterial blood in the lungs, 

 by which carbonic acid gas is formed ; yet, 

 while the greater part of the absorbed gas is 

 held in solution in the arterial blood, a small 

 portion of it may enter into chemical combi- 

 nation in a manner hitherto not definitely 

 ascertained.* 



It is almost universally believed that the 

 free carbonic acid gas in the blood is formed 

 by the combination of the absorbed oxygen 

 with carbon in the blood, chiefly if not en- 



arterial blood to the capillaries is decomposed during 

 the nutritive processes, and carbonic acid is formed 

 and held in solution in the blood. 



[Dr. G. O. Rees has lately put forward the following 

 ingenious theory of respiration. He finds by analysis 

 that the corpuscles of venous blood contain fatty 

 matter in combination with phosphorus, which does 

 not exist in arterial blood, or, at most, is found in it 

 only in very small quantity. In respiration the oxy- 

 gen of the inspired air unites with this phosphorus 

 and fatty matter, and a combustion of it takes place, 

 of which the products are water and carbonic acid, 

 from the union of the oxygen with the elements of 

 the fatty matter, and phosphoric acid, from the union 

 of the oxygen with the phosphorus. The carbonic 

 acid and water are exhaled, and appear in the 

 expired air; the phosphoric acid attracts the soda 

 of the liquor sanguinis from its combination with 

 albumen and lactic acid, and thus forms a tribasic 

 phosphate of soda, a salt which possesses in a marked 

 degree the property of giving a bright colour to 

 hffiinatosine. See Dr. Rees' paper in the Lond. Edin. 

 and Dubl. Phil. Mag. for July, 1848. ED.] 



* Marchand (Journal fiir praktische Chemie, Band 

 xxxv. S. 385. 1845) in his experiments found that 

 oxygen gas does not unite with fibrin to form car- 

 bonic acid until it has been exposed to its action for 

 some days, in fact not until it is passing into a state 

 of putrefaction ; and that, on subjecting to a conti- 

 nuous current of oxygen gas, the red corpuscles, and 

 beaten venous blood, after all the free carbonic acid 

 held in solution had been carefully separated by the 

 air-pump and agitation with hydrogen, no carbonic 

 acid gas was evolved. These experiments invalidate 



tirely in the course of its circulation through 

 the systemic capillaries ; but this opinion, 

 however plausible it may appear, and though 

 it apparently accounts fur the evolution of 

 animal caloric in a satisfactory manner, does 

 not rest upon any direct evidence. There 

 are no facts that militate against the exist- 

 ence of such a combination, and there can be 

 no doubt that in the present state of our 

 knowledge it affords the readiest and most 

 complete interpretation of the phenomena 

 referred to it, but still it is quite possible that 

 the carbonic acid may be formed during the 

 process of nutrition differently from what is 

 generally supposed. 



Cause of the change of colour in the blood. 

 The manner in which the changes of colour 

 in the blood is effected as it passes through 

 the pulmonic and systemic capillary vessels, 

 has not yet been satisfactorily determined. 

 It seems now to be pretty generally admitted 

 that the hasmatosine or colouring matter of 

 the blood is enclosed within the enveloping 

 membrane of the red corpuscles ; that this 

 haematosine, though it may be combined with 

 iron, does not derive its colour from the pre- 

 sence of this metal ; and that all attempts to 

 explain the change in the colour of the blood 

 in the lungs by the formation of certain 

 oxides and salts of iron must be abandoned. 

 It is well known that various substances, 

 besides oxygen gas, can impart a bright red 

 colour to venous blood when mixed with it, 

 and without being attended with any evo- 

 lution of carbonic acid gas. The best known 

 of these are solutions of the sulphate of soda, 

 nitrate of potass, phosphate of soda, carbon- 

 ate of soda, carbonate of potass, and sugar. 



The opinion of Stevens *, that the change 

 from the venous to the arterial hue in the 

 blood is to be attributed to the actions of the 

 salts dissolved in the blood upon the haemato- 

 sine, after the removal of the free carbonic 

 acid of the venous blood through the attrac- 

 tive force of the oxygen of the atmospheric 

 air, has not been confirmed by subsequent 

 researches. It has been ascertained that the 

 removal of carbonic acid from venous blood, 

 by means of the air-pnmp f , or by agitation 



the inferences in favour of the opinion, that the 

 oxygen absorbed at the lungs partly enters into 

 combination with the constituents of the blood in the 

 lungs and forms or liberates carbonic acid gas, drawn 

 from the experiments of Scherer (Annalen der Che- 

 mie und Pharmacie, Band xl. 1841) upon the action 

 of oxygen gas upon fibrin, and those of Berzelius 

 (Lehrbuch der Chemie, Band iv. S. 94. 1831), and 

 Maack (De Ratione quse Colorem Sanguinis inter, 

 &c., p. 35. Kilias 1834) upon the greater absorbing 

 power for oxygen of the colouring matter of the 

 blood over the serum. Mulder (Hollandische Beit- 

 rage, &c. Band i. heft i. B. '20. 184(5) adduces various 

 arguments to show that the experiments of Magnus, 

 and they apply equally to those of Marchand, by no 

 means prove that a part of the oxygen absorbed at 

 the lungs does not enter into chemical combination 

 with the constituents of the blood before it reaches 

 the capillaries of the systemic circulation. 



* London Philos. Transact, vol. xlvi. p. 345. 

 1835. 



f Dr. J. Davy and others. 



