THE PROCESS OF EXCITATION 111 



entire carbon dioxide production during a period of many hours. 

 No conclusions can be drawn from this as to the conditions 

 existing in the first period of time, directly after the animals 

 have been subjected to an atmosphere of nitrogen. It is quite 

 possible that subsequent to the change to nitrogen an oxydative 

 carbon dioxide formation may have continued in decreasing 

 degree, without this being shown in the final result. The prob- 

 lem of the existence of a reserve supply of oxygen is in no way 

 solved by these experiments. 



In assuming the presence of a reserve supply of oxygen in the 

 cell we must above all entertain no false conception as to its 

 amount. This must be, as I have often had occasion to empha- 

 size, exceedingly small and in no way comparable with the great 

 masses of organic reserve substances contained in the cell. The 

 assumption, especially for the nerve centers of the frog, that the 

 excitability remains after complete exclusion of oxygen must be 

 looked upon as demonstrating a reserve supply of oxygen, would 

 oblige one to suppose the presence of such a small store of oxygen 

 that it would be completely exhausted by continued activity in 

 room temperature within ten to twenty-five minutes. Strych- 

 ninized frogs, in which the blood has been replaced by an oxygen- 

 free saline solution, lose, as I have shown,^ their excitability com- 

 pletely within ten to twenty-five minutes after the blood has 

 been displaced. Nevertheless the assumption of the existence of 

 a small oxygen supply in the cell can hardly be evaded. It must 

 not be imagined that the moment the blood of the frog has been 

 replaced with an oxygen-free solution, there is not a trace of 

 oxygen left in the organism. Were such the case, the irritability, 

 if measured by the extent of the response, would sink momenta- 

 rily to a very low level, for the anoxydative disintegration pro- 

 cesses are associated v/ith an incomparably smaller production of 

 energy than those of oxydative disintegration. We see, however, 

 that the irritability in the muscles, nerves and nerve centers of the 

 frog even after the complete withdrawal of oxygen at first re- 

 mains practically at the former height and only very gradually 



1 Max Verworn: "Ermudung, Erschopfung und Erholung der nervosen Centra des 

 Riichenmarka." Arch. f. Anat. u. Physiol, physiol. Abt. Suppl. 1900. 



