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which give more or less odor to the breath, 

 and these, with the carbonic acid, etc., are 

 exhaled by the animal with every breath. 

 Now, the result of this combustion of 

 material in the lungs is, as in the stove, 

 productive of heat and here we find the 

 great source of animal heat. Every time 

 the animal takes in a breath of air, it con- 

 sumes a portion of the oxygen of the air, 

 in making heat and carbonic acid, and as 

 this process goes on, ten or fifteen times a 

 minute, the air in a circumscribed space, 

 as in a close room or stable, becomes rap- 

 idly exhausted of oxygen and overloaded 

 with carbonic acid and other impurities, 

 and less and less fit to carry on the vital 

 processes. New oxygen must be supplied, 

 and the carbonic acid blown away. If it 



