LECT. VI. NATURE OF ARTERIALIZATION. 125 



this gas through a liquid formed of blood dissolved in 

 water, and you find that it will soon become black. This 

 blackish liquid, being placed in a flask filled with oxygen, 

 and agitated for a few moments, looses its deep colour and 

 acquires a vermilion tint. Sulphuretted hydrogen is the 

 only body, which having acted on the blood, even in very 

 small quantities, renders this fluid incapable of being arte- 

 rialized by oxygen. 



Since the time of Priestley it has been known, that if 

 blood, which has become blackish from the action of car- 

 bonic acid, be put into a moist bladder which is placed in 

 contact with oxygen, the blood again becomes red, the 

 interposed membrane not preventing the change of colour. 



It is then proved, by experiment, that the- change from 

 black to red in the colour of the blood, which constantly 

 accompanies the introduction of oxygen into the air ves- 

 sels of living animals, under circumstances identical with 

 those which I have pointed out, is a phenomenon entirely 

 physico-chemical, and consists in the action of oxygen 

 upon a liquid which has its origin in the living organism. 



Nature of Arterialization. What, then, is the nature of 

 this change ? What are the laws which govern it? Here 

 are the details which must still engage us ; and in such 

 investigations we shall rely on the splendid researches of 

 Magnus. 



If we receive the venous blood, which escapes from an 

 aperture in the vein of a living animal, in a vessel contain- 

 ing pure hydrogen gas, and shake the two together, we 

 shall find in the vessel some carbonic acid. This certainly 

 cannot be the result of the chemical combination of hy- 

 drogen with the elements of the blood ; nor can it be sup- 

 posed that the acid was expelled from the blood by the 

 affinity of hydrogen, for the body with which we may fancy 

 the carbonic acid was combined. The carbonic acid, 



