256 THEORY OF RESPIRATION. 



sary to animal life ; and, since physiology has proved, 

 that the globules take no share in the process of nutri- 

 tion, it cannot be doubted that they play a part in the 

 process of respiration. 



The compound of iron in the globules has the char- 

 acters of an oxidized compound ; for it is decomposed 

 by sulphuretted hydrogen, exactly in the same way as 

 the oxides or other analogous compounds of iron. By 

 means of diluted mineral acids, peroxide (sesquioxide) 

 of iron may be extracted, at the ordinary temperature, 

 from the fresh or dried red coloring matter of the blood. 



The characters of the compounds of iron may, per- 

 haps, assist us to explain the share which that metal 

 takes in the respiratory process. No other metal can 

 be compared with iron, for the remarkable properties of 

 its compounds. 



The compounds of protoxide of iron .possess the 

 property of depriving other oxidized compounds of 

 oxygen ; while the compounds of peroxide of iron, 

 under other circumstances, give up oxygen with the 

 utmost facility. 



Hydrated peroxide of iron, in contact with organic 

 matters destitute of sulphur, is converted into carbonate 

 of the protoxide. 



Carbonate of protoxide of iron, in contact with wa- 

 ter and oxygen, is decomposed ; all the carbonic acid 

 is given off, and, by absorption of oxygen, it passes in- 

 to the hydrated peroxide, which may again be convert- 

 ed into a compound of the protoxide. 



