BLOOD. 133 



state of solutiou. The blood-corpuscles absorb from this con- 

 stant source a due supply of oxygen for their change. 



The metamorphosis occurs in the peripheral system, and, for 

 the most part, in certain organs, as, for instance, the kidneys. 

 The blood-corpuscles give up the carbonic acid, thus formed, 

 to the blood, and it is thrown off by the lungs. It must 

 be remembered that blood always contains carbonic acid and 

 oxygen, but arterial contains more of the latter and less of the 

 former than venous blood ; also, that the whole of the carbonic 

 acid is not separated by the lungs, although, when the blood 

 reaches those organs, it is perfectly free from oxygen. 



Although the atmospheric air and the circulating fluid are 

 not brought into absolute contact, there is no impediment to 

 their mutual action. The absorption of the air through the 

 humid membrane that surrounds the parenchyma of the lungs 

 is facilitated by the immense extent of surface presented, 

 over the whole of which a thin stratum of blood is distributed, 

 and simultaneously exposed to the atmospheric influence. The 

 permeability of the soft tissues, especially of the membranes, 

 by fluid and gaseous substances, is a well known fact. It 

 is in accordance with this law that atmospheric air finds its 

 way into the blood. Dark red blood, inclosed in a moist 

 bladder, soon assumes a bright red tint ; a gas inclosed in a 

 similar receptacle is found, after some time, to be partly dis- 

 placed by atmospheric air. These are mere illustrations of the 

 same principle. If the opinion that has just been given be 

 correct, then carbonic acid and oxygen must be present both 

 in venous and arterial blood. Numerous experiments have 

 been instituted with the view to determine this point. 



By submitting 13 ounces of the venous blood of a calf to a 

 heat of 200^, Sir H. Davy obtained I'l cubic inch of carbo- 

 nic acid, and 0'7 of oxygen, and the experiment has been con- 

 firmed by Brande and Vogel. Stromeyer, Bergemann, ^Miiller, 

 and others have failed in obtaining carbonic acid from blood 

 in this manner. Brande and Yogel found that blood placed in 

 vacuo developed a gas which contained some carbonic acid, and 

 their statement is confirmed by Home, Bauer, and Reid Clanny, 

 while J. Da^y,l INIitscherlich, Tiedemann, Gmelin, and Miiller 



' [Dr. Davy has recently shown that gas is frequently, although not invariably, 

 disengaged both from venous and arterial blood in vacuo. Researches, Physiol, and 

 Anat. vol. 2, p. 153.] 



