DR. DAVY'S ACCOUNT OF SOME EXPERIMENTS ON THE BLOOD. 291 



with the supertartrate of potash ; and if evaporated to dryness over sulphuric acid 

 under an exhausted receiver, on being subjected to heat, it disengages carbonic acid 

 gas. 



IV. Does the blood contain any gas capable of being extricated by the air-pump ? 



On this subject also there has been much difference of opinion. Our distinguished 

 countryman Mayow, more than a century ago, stated tliat blood, especially arterial 

 blood, effervesces in vacuo, which he attributed to the disengagement of air, his Spi- 

 ritus Nitro-aereus*. Sir Everard Home, on the authority of Mr. Brande, in 1818, 

 asserted that blood, both venous and arterial, under the exhausted receiver evolves a 

 large quantity of carbonic acid gas, an ounce of blood as much as two cubic inches 

 of gas-f-. I repeated the experiment shortly after, but without confirming the result; 

 neither by the air-pump, nor by heat applied even to coagulation of blood and serum 

 in close vessels, did I succeed in demonstrating the extrication of this acid J. Since 

 that time the experiment of the air-pump on the blood has been frequently made, and 

 by observers of great accuracy, as by Drs. Duncan and Christison in this country, 

 by MM. Tiedeman, Gmelin, Mitschenlich and Muller on the continent, and re- 

 cently by MM. BiscHOFF and Magnus. With the exception of the last-mentioned 

 inquirers, the results have been negative. MM. Bischoff and Magnus, on the con- 

 trary, state that by careful exhaustion they have obtained gas from the blood ; the 

 former a small quantity of carbonic acid gas, the latter a notable quantity, and not 

 only of carbonic acid gas, but also of oxygen and azote §. 



M. Magnus attributes the failures of former experimenters to their having used 

 pumps of imperfect exhausting power, or to their not having carried the exhaustion 

 suflSciently far. In my early and first trial I employed the air pump belonging to 

 the laboratory of the Royal Institution, which was an excellent one, and which I then 

 believed was in good order ; but I might have been mistaken. 



To endeavour to satisfy myself on this point, I have had an air-pump constructed 

 for the purpose, under the direction of an able artist, Mr. Ross, of 33 Regent Street, 

 already distinguished for his excellent achromatic microscopes, and it has answered 

 perfectly. When the exhaustion has been carried as far as possible, the difference of 

 level of the mercury in the siphon-gauge has not exceeded a quarter of an inch, and 

 over water has not exceeded half an inch. 



Experimenting with this machine on blood, collected with such precautions as I 

 believe to have been adequate to insure accuracy of results, in a majority of instances 

 the disengagement of gas has been rendered manifest, and both from arterial and 

 venous blood. 



* JoHANNis Mayow Opera omnia. Hagse Com. 1681. p. 133. 

 t Philosophical Transactions for 1818, p. 181. 

 I Ibid. 1823, p. 516. 



§ Annales des Sciences Nat. torn. viii. p. 79. et seq. contain a translation of M. Magnus' paper, with a figure 

 of the apparatus, &c. used ; the original appeared in Poggkndoef's Journal, vol. xl. part 3, 



2 p2 



