THE PURIFICATION OF THE BLOOD, ETC. 35 



animal, vegetable, and mineral bodies. The 

 water of the ocean, or of rivers, or of lakes, is 

 by the atmospheric pressure replete with air, 

 and is moreover composed of oxygen and hydro- 

 gen. Of one million of cubic inches of pure air, 

 the weight of the oxygen is 71,809*3, of azote 

 238,307-7, total 310,117-0. Oxygen, then, is 

 the food of life, and every animal destroys vast 

 quantities of this food, insomuch that if the 

 great vegetable kingdom did not produce 

 oxygen, and fix carbonic acid, the atmosphere 

 itself would in due time be incapable of sustain- 

 ing life. As a proof of this, we may state that 

 if any air-breathing animal, especially quad- 

 ruped or bird, (for lower animals do not con- 

 sume oxygen so rapidly,) be placed in a vessel 

 of atmospheric air, so sealed up as to prevent all 

 communication with the circumambient atmo-* 

 sphere, the animal, after a given lapse of time, 

 perishes, and the oxygen of the air in which it was 

 confined will be found exchanged for carbonic 

 acid. 



This leads us to the point in hand. The 

 venous blood, having passed through the arterial 

 system, and fulfilled the demands of that system, 

 becomes replete with carbon, the presence of 

 which renders it unfit for the purposes of life. 

 Whence it acquired this carbon, or carbonic acid, 

 is not very clear. " Some observations lately 

 made," says Dr. Prout, " have induced us to be- 

 lieve that the conversion of albuminous matters 

 into gelatine is one great source of the carbonic 

 acid in venous blood. Gelatine contains three or 



