CONDUCTIVITY 



131 



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Fig. 21. 



Course of the action current of the nerve. The thin line indicates the action current 

 produced by a weak, the thick line the action current produced by a strong stimulus. 

 The duration of the action current is the same in both cases. (After Cotch.) 



resulting from the application of strong electrical stimuli, to a 

 spreading out of the "Stromschleifen" from the point of appli- 

 cation and consequently there is a shortening of the stretch of 

 nerve between the point of stimulation and the indicator. 



This conspicuous difference in the conduction of the two 

 extreme types of living substance, which we have already ob- 

 served, arouses the question as to what properties of living sub- 

 stance bring about these differences. In order to answer this 

 question, it is necessary, first of all, to make some general state- 

 ments concerning the processes of conductivity. 



As already emphasized, all living substance possesses the capa- 

 bility of conducting excitations to a definite degree. We may, 

 therefore, assume that the same fundamental property of con- 

 ductivity exists in all substances. A fact to be considered in the 

 conduction of excitation, is that the primary breaking down of 

 the complex molecules at the position of stimulation act in turn 

 as exciting stimuli upon the neighboring portion of the living 

 substance, which in turn undergoes a similar decomposition. And 

 so this process continues. This fact is evident from the observa- 

 tions on the process of excitation. But the nature of the stimulus 



