PROPERTIES OF 



EXPERIMENT III. 



Having laid bare the jugular vein of a living rabbit, I tied 

 it up in three places ; then opening it between two of the liga- 

 tures, I let out the blood, and filled this part of the vein with 



colour between the blood of the pulmonary artery and vein ; and though 

 he observed that the blood of the crural artery is brighter than that of 

 the vein, he denied that the difference of colour is caused by the action 

 of the lungs. Cigna 1 refuted the error that the lower part of the blood- 

 clot is darkened by the sinking of the heavier and blacker corpuscles. 

 He gave some experimental proofs of the brightening effect of air on the 

 colour of the blood ; but believed that the air is not introduced through 

 the lungs, their chief office being, as he thought, for exhalation and to 

 cool the blood. Dr. PriestleyJ ascertained the correctness of Lower's 

 results, and that air will act on the blood through a moist membrane. 

 Priestley also proved k that the brightening of the blood is produced by the 

 oxygen only, and that carbonic acid, hydrogen, and azote, have the 

 contrary effect. 



More recently, Dr. Stevens 1 has arrived at the very different conclusion, 

 that the bright colour of arterial blood is caused chiefly or entirely by 

 the agency of the salts of the serum on the hematozine ; and that oxygen 

 changes the colour of blood from venous to arterial, merely by re- 

 moving the carbonic acid which is the cause of the dark hue of venous 

 blood. Dr. Turner 111 fully adopts these views ; and Mr. Hoffmann 

 is also favorable to them, chiefly because he found that salt alone 

 will render black blood florid, while air without salt will not pro- 

 duce the effect, as he illustrates by a bit of clot rendered dark 

 by distilled water. I find that the clot, darkened by washing with 

 water, is also made florid by sugar, though less brightly and quickly 

 than by the salt. Dr. Christison, on agitating red corpuscles and 

 serum of blood with atmospheric air, always found that oxygen disap- 

 pears while carbonic acid is formed ; but, owing to the strong solvent 

 power of the serum on this acid, he believed that more of it was formed" 

 than appeared in the residual air. In all these experiments venous 

 blood acquired a bright vermilion hue, and arterial blood had its florid 

 tint heightened. Dr. Davy p obtained the same results as to the absorp- 

 tion of oxygen by the blood and the consequent brightening of its colour. 

 But in the residual air he could detect only a trace of carbonic acid, 

 not exceeding one per cent. ; and none at all when, instead of common 

 air, pure oxygen was agitated with the blood. He observed that venous 



1 Miscel. Phil. Math. Taurinensis, t. i, 4to, m Elements of Chemistry, 5th ed. p. 972, 



1759; et Melanges de la Soc. Roy. 8vo, Lond. 1834. 



de Turin, torn, v, 1770-3. n Lond. Med. Gaz. xi, 1833, p. 887. 



J Phil. Trans. 1776, Ixvi, 239. Edin. Med. and Surg. Journ. xxxv, 

 k Exp. and Obs. on different kinds of Air, 97-100. 



8vo, Birmingham, 1790, iii, 363. P Phys. and Anat. Res. ii, 138-9, 176- 

 1 On the Blood, p. 27, 8vo, Lond. 1832 ; 182. 



Phil. Trans. 1835, p. 352, et seq. 



