182 IRRITABILITY 



clearly recognized. Fatigue is simply the refractory period pro- 

 longed by deficiency of oxygen. In both cases there is a diminu- 

 tion of irritability. In both cases this diminution is conditioned 

 by a retardation of oxydative disintegration following every 

 stimulation. In both cases it is the relative deficiency of oxygen 

 which produces this delay. In both cases the oxydative decompo- 

 sition can be quickened and irritability restored, that is, the refrac- 

 tory period lessened and fatigue removed by a sufficient supply of 

 oxygen. The amount of oxygen which suffices to constantly main- 

 tain the specific irritability of a living system in an undisturbed 

 metabolism of rest is not sufficient if the system is continuously 

 functionally activated by stimulation. The refractory period 

 increases after excitation and merges, although very gradually, 

 finally into permanent nonirritability, that is, into complete 

 fatigue. 



The knowledge that fatigue represents a prolonged refractory 

 period resulting from relative deficiency of oxygen has enabled 

 me with the aid of my coworkers to demonstrate the existence 

 of fatigue and produce the typical symptoms experimentally for 

 a living tissue, which up to then was considered indefatigable: 

 I refer to the medullated nerve. After having found that the 

 condition necessary for the production of fatigue in the nervous 

 centers is a deficiency of oxygen, I arrived at the conclusion that 

 fatigue could only be obtained in the medullated nerve when sub- 

 jected to a deficiency of oxygen. Up to that time, however, no 

 consumption of oxygen was known for the nerve. It was, there- 

 fore, necessary to first ascertain if the nerve possessed an oxyda- 

 tive metabolism. At my request, H. von Baeyer investigated these 

 questions. After many vain attempts to obtain absolutely pure 

 nitrogen, we finally succeeded in finding a method by which it is 

 possible to gain nitrogen gas, which is, one might almost say, in 

 a mathematical sense absolutely pure. It was then possible for 

 H. von Baeyer^ to asphyxiate the nerve and subsequently to bring 

 about complete restoration by the introduction of oxygen. It 

 was shown that the nerve requires merely a minute quantity of 



1 Hidetsurumaru Ishikawa: "Ueber die scheinbare Bahnung." Zeitschr. f. allgem. 

 Physiologie Bd. Ill, 1904. 



