CHAPTER VII 



THE REFRACTORY PERIOD AND FATIGUE 



Contents: Conception of specific irritability. Alteration of specific irri- 

 tability during and after excitation. Refractory period in various 

 forms of living substance. Absolute and relative refractory period. 

 Curve of irritability during refractory period. Dependence of the 

 duration of the refractory period on the rapidity of the course of the 

 metabolic processes in the living substance. Dependence on tempera- 

 ture. Dependence on supply of oxygen. Theory of refractory period. 

 Refractory period as basis of fatigue. Fatigue as a form of asphyxia- 

 tion. Alterations of irritability and the course of excitation in fatigue. 

 Recovery from fatigue. The role played by oxygen in recovery. 

 Fatigue as an expression of the prolongation of the refractory period 

 conditioned by the relative want of oxygen. Fatigue of the nerve. 



Every living system possesses, as we know, a peculiar and char- 

 acteristic manner of reacting to stimulation. The muscle responds 

 with a contraction, the salivary cell with production of saliva, the 

 luminous cell with the emission of light. This is the specific 

 energy in the sense of Johannes Muller. Every living system is 

 likewise characterized by a certain degree of irritability, which 

 can be expressed by the threshold value of the stimulus at which 

 the specific reaction is just perceptible. This degree of irrita- 

 bility, by which the system concerned is distinguished, may be 

 termed its specific irritability. 



From the standpoint of the conditional method of investigation 

 it is at once apparent that specific energy, as well as specific irri- 

 tability, must be solely determined by the specific conditions exist- 

 ing in the particular system. It follows from this that every alter- 

 ation in the conditions of the system, that is, every change of its 

 state, likewise entails a corresponding alteration of its specific 

 energy and its specific irritability. It is, therefore, self-evident 

 that the alteration of the state, which is undergone by the living 



