THEORY OF RESPIRATION. 259 



expired than at other times. In all cases, where the 

 oxygen of the arterial globules has been partly ex- 

 pended, otherwise than in the formation of carbonic 

 acid, the amount of this latter gas expired will corre- 

 spond exactly with that which has been formed ; less, 

 however, will be given out after the use of fat and of 

 still wines, than after champagne. 



According to the views now developed, the globules 

 of arterial blood, in their passage through the capilla- 

 ries, yield oxygen to certain constituents of the body. 

 A small portion of this oxygen serves to produce the 

 change of matter, and determines the separation of 

 living parts and their conversion into lifeless com- 

 pounds, as well as the formation of the secretions and 

 excretions. The greater part, however, of the oxy- 

 gen is employed in converting into oxidized compounds 

 the newly formed substances, which no longer form 

 part of the living tissues. 



In their return towards the heart, the globules which 

 have lost their oxygen combine with carbonic acid, 

 producing venous blood ; and, when they reach the 

 lungs, an exchange takes place between this carbonic 

 acid and the oxygen of the atmosphere. 



The organic compound of iron, which exists in ven- 

 ous blood, recovers in the lungs the oxygen it has lost, 

 and, in consequence of this absorption of oxygen, the 

 carbonic acid in combination with it is separated. 



All the compounds present in venous blood, which 

 have an attraction for oxygen, are converted, in the 



