270 THEORY OF RESPIRATION. 



For every volume of oxygen which the globules 

 can give off, there will be formed (as carbonic acid 

 contains its own volume of oxygen, without conden- 

 sation) neither more nor less than an equal volume 

 of carbonic acid. For every volume of oxygen 

 which the globules are capable of absorbing, no 

 more carbonic acid can possibly be separated than 

 that volume of oxygen can produce. 



When carbonate of protoxide of iron, by the 

 absorption of oxygen, passes into the hydrated 

 peroxide, there are given off, for every volume of 

 oxygen necessary to the change from protoxide to 

 peroxide, four volumes of carbonic acid gas. 



But from one volume of oxygen only one volume 

 of carbonic acid can be produced ; and the absorption 

 of one volume of oxygen can only cause, directly, 

 the separation of an equal volume of carbonic acid. 

 Consequently, the substance or compound which has 

 lost its oxygen, during the passage of arterial into 

 venous blood, must have been capable of absorbing or 

 combining with carbonic acid ; and we find, in point 

 of fact, that the living blood is never, in any state, 

 saturated with carbonic acid ; that it is capable of 

 taking up an additional quantity, without any appa- 

 rent disturbance of the function of the globules. 

 Thus, for example, after drinking effervescing wines, 

 beer, or mineral waters, more carbonic acid must 

 necessarily be expired than at other times. In all 

 cases, where the oxygen of the arterial globules has 

 been partly expended, otherwise than in the forma- 



