396 OXYGEN AND CARBON. 



really acquires new properties, from its exposure to the 

 air with which the cells of these organs are filled. By 

 a true chemical process, the oxygen is separated from 

 the air, that oxygen is made to combine with the carbon 

 and hydrogen, and carbonic acid and water are formed. 

 These are liberated and thrown off from the body either 

 through the lungs or by the skin. In the processes of 

 life, as far as we are enabled to trace them, we see 

 actions going on which are referred to certain causes 

 which we appear to explain. Thus, the combination of 

 the oxygen of the air with the carbon of the blood is 

 truly designated a case of chemical affinity ; and we 

 find that in endeavouring to imitate the processes of 

 nature in the laboratory, we are, to a certain extent, 

 successful. We can combine carbon and oxygen to 

 produce carbonic acid ; and we know that the result of 

 that combination is the development of certain definite 

 quantities of heat. Let us examine the conditions of 

 this chemical phenomenon, and we shall find that in the 

 natural and artificial processes, for we must be allowed 

 to make that distinction, there are analogous circum- 

 stances. If we place a piece of pure carbon, a lump of 

 charcoal or a diamond, in a vessel of air, or even of pure 

 oxygen gas, no change will take place in either of these 

 elements, and, however long they may be kept together, 

 they will still be found as carbon or diamond, and 

 oxygen gas. If we apply heat to the carbon until it 

 becomes incandescent, it immediately begins to com- 

 bine with the oxygen gas, it burns ; after a little 

 time all the carbon has disappeared, and we shall find, 

 if the experiment has been properly made, that a gas is 

 left behind which is distinguished by properties in every 

 respect the reverse of those of oxygen, supporting neither 

 life nor combustion, whereas oxygen gives increased 

 vigour to both. We have now, indeed, carbonic acid 

 gas formed by the union of the two principles. 



A dead mass of animal matter may be placed in 



