180 IRRITABILITY 



remains a certain amount of shortening, when the next contraction 

 begins. This characteristic extension of the individual contraction 

 curve of the fatigued muscle is an expression of the retardation 

 of the oxydative disintegrating processes and of the Treppe. It 

 shows us that fatigue is perceptible to a slight degree even after 

 the first excitation. After every succeeding stimulus the oxyda- 

 tive decomposition in the fatigued muscle is increasingly pro- 

 longed. It is, therefore, self-evident that the capability of action 

 of the muscle likewise becomes less with increasing fatigue. 

 Every state of fatigue is, in fact, distinguished by the decrease of 

 response. This is perceptible in the later stages by the decline of 

 the height of contraction. Hence all symptoms of fatigue which 

 we observe form the expression of one single process ; it is the 

 constantly increasing slowness of oxydative disintegration with 

 increasing fatigue. 



Exactly similar conditions as those of the muscle are seen in 

 the central nervous system. The reflex contraction of the triceps 

 of the frog produced by 'stimulation of the central end of the 

 sciatic nerve with single induction shocks demonstrates clearly 

 as Ishikawa 1 has proved in certain stages of fatigue, an increase 

 in height and a strong relaxation which does not depend upon the 

 fatigue of the muscle but on that of the centers. If the fatigue 

 is greater, the height of the contraction then decreases, whereas 

 the extension of the course of relaxation increases further. The 

 possibility of fatigue of the muscle during these experiments was, 

 of course, precluded by proper precautionary measures. Irri- 

 tability and the course of excitation in fatigue of the centers 

 show exactly the same alterations as developed in fatigue of the 

 muscle. The processes of oxydative breaking down are retarded 

 more and more with increasing fatigue, that is, fatigue is charac- 

 terized by exactly the same processes as is the prolongation of 

 the refractory period by the deficiency of oxygen, and likewise 

 in fatigue this retardation of the oxydative disintegration pro- 

 cesses is conditioned by the relative deficiency of oxygen. This 

 is shown by the role played by oxygen in recovery after fatigue. 



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

 Physiologic Bd. XI, 1910. 



