ORGANIC CHEMICAL PROCESSES. 55 



fitted for its peculiar functions. A cubic inch of 

 sulphuretted hydrogen introduced into the lungs, 

 would cause instant death, but it is formed, under 

 a variety of circumstances, in the intestinal canal 

 without any injurious effect. 



In consequence of such transformations as we 

 have described, excrements are formed of various 

 composition; some of these contain carbon, in 

 excess; others nitrogen, and others again hydrogen 

 and oxygen. The kidneys, liver, and lungs, are 

 organs of excretion; the first separate from the 

 body all those substances in which a large propor- 

 tion of nitrogen is contained; the second, those 

 with an excess of carbon ; and the third, such as 

 are composed principally of oxygen and hydrogen. 

 Alcohol, also, and the volatile oils which are inca- 

 pable of being assimilated, are exhaled through the 

 lungs, and not through the skin. 



Respiration must be regarded as a slow process 

 of combustion or constant decomposition. If it be 

 subject to the laws which regulate the processes of 

 decomposition generally, the oxygen of the inspired 

 air cannot combine directly with the carbon of com- 

 pounds of that element contained in the blood; the 

 hydrogen only can combine with the oxygen of the 

 air, or undergo a higher degree of oxidation. Oxy- 

 gen is absorbed without uniting with carbon ; and 

 carbonic acid is disengaged, the carbon and oxygen 

 of which must be derived from matters previously 

 existing in the blood. 



