THE REFRACTORY PERIOD AND FATIGUE 177 



say, the individual alterations produced by the want of oxygen, 

 that is, the restriction and retardation of the oxydative disinte- 

 gration, the corresponding increase of the anoxydative decompo- 

 sition and the accumulation of the products of incomplete oxyda- 

 tion and anoxydative breaking down have the same influence in 

 that they decrease the strength of the response and retard the 

 rapidity of the decomposition process. These are the general 

 effects perceptible in the refractory period by the deficiency of 

 oxygen. 



The establishment of these facts of the dependence of the re- 

 fractory period upon oxygen are of the utmost importance for 

 the genesis of fatigue, for the state of fatigue in all aerobic organ- 

 isms is invariably brought about by deficiency of oxygen. In 

 other words : fatigue is invariably asphyxiation. A deficiency of 

 organic reserve substances never occurs in fatigue before the 

 effect of oxygen deficiency leads to complete depression, for the 

 quantity of organic reserve substances at the disposal of the cells 

 is greater comparatively than that of oxygen. This is shown by 

 transfusion experiments in which the time involved before com- 

 plete paralysis was brought about in the frog by the introduction 

 of an oxygen-free saline solution was ascertained and compared 

 with the period which elapsed before complete paralysis took 

 place, when the same solution saturated with oxygen was used. 



Although the previously described experiments on the strych- 

 ninized frog show clearly the relations of fatigue to the refractory 

 period, I should, nevertheless, like to illustrate them somewhat 

 further. 



The state of fatigue as it is developed in a living system by a 

 continuous functional activity is characterized by a series of 

 symptoms which can be best studied in the fatigue of the muscle, 

 the nervous centers, and the peripheral nerves. 



If the muscle of the frog is isolated and rhythmically stimu- 

 lated with single induction shocks and the muscle contractions 

 graphically recorded, it will be found that the first perceptible 

 alteration during the course of stimulation is the increasing 

 height in the curve, which appears directly after the first 

 contraction and becomes more and more noticeable after every 



