THE GASEOUS EXCRETION. 39 l 



quickly. These changes follow one upon the other rather 

 rapidly. In the oxygen-absorbing stage some intermediate 

 products are probably built up from sugar or glycogen or other 

 substances, which fall apart with liberation of water and car- 

 bon dioxide in the succeeding active condition of the muscle. 

 The problem of oxidation in the tissues is possibly somewhat 

 like that of etherification in which alcohol yields ether indi- 

 rectly through the intermediate ethyl sulphuric acid, and sev- 

 eral suggestions have been brought forward as to the character 

 of complexes formed in one stage of the oxidative metabolism 

 to be decomposed in another. At the present time these sug- 

 gestions are practically wholly within the realm of speculation, 

 and not therefore suitable for presentation in this place. It 

 is likely that all these reactions, which seem to be carried on 

 in the tissues rather than in the fluids of the body, are incited 

 by enzymic ferments, and to-day certain classes of oxidases 

 are often assumed to be the agents active in the changes. For 

 some of the oxidations it has been pretty well settled that an 

 enzyme produced by the pancreas is necessary. 



