CONDUCTIVITY 139 



reality and would thus transfer the difficulty to the ultimate 

 fiber unit, for which a homogeneous molecular structure would 

 have to be presumed. In short, whatever may be the assumption 

 on which molecular structure of elementary fibers is based, the 

 fact of the decrementless conduction peremptorily demands, from 

 the physical standpoint, that from cross section to cross section 

 the entire number of irritable molecules are broken down. This 

 conclusion is highly important, for it indicates very clearly that 

 the "all or none law" is applicable to the nerve. 



This gives us occasion to return to the discussion of the ques- 

 tion, if living systems really exist which respond in accordance 

 with the "all or none law." The medullated nerve forms an 

 object particularly suited to serve as a starting point for the 

 treatment of this especially important problem. The question 

 arises in this connection, if the validity of this law for the nerve 

 can be tested by other means. 



At first it would seem as if the application of the "all or none 

 law" to the nerve were in contradiction to the well-known fact 

 that a weak stimulation of the nerve produces a weak, a strong 

 stimulation, a strong response. In this connection Gotch 1 has 

 pointed out, as the result of experimental studies of the wave 

 of activity of the nerve, that the difference in response, follow- 

 ing the application of stimuli of varying strengths, is under- 

 standable from the fact that threshold stimuli stimulate only a 

 few of the fibers of the nerve trunk, whereas progressively in- 

 creasing the intensity of the current involves more and more 

 fibers. There can be no doubt that this factor explains the differ- 

 ence in the strength of the response. Therefore, in reality we 

 do not find here a contradiction of the "all or none law." On 

 the other hand, the fact that the nerve, in contradistinction to 

 many other forms of living substance, the ganglion cell, for 

 example, upon a weak stimulation does not show the phenomena 

 of summation, even when the stimuli follow each other in a 

 rapid succession, indicates very strongly that the weakest oper- 

 able stimulus produces maximal excitation, so that the response 



1 Gotch: "The submaximal electrical response of nerve to a single stimulus." 

 Journal of Physiology, Vol. XXVIII, 1902. 



