148 IRRITABILITY 



which assumes that the atom groups capable of breaking down 

 are joined together by a chemical linking of atoms to long fiber- 

 shaped giant molecules through the whole nerve fiber, for this 

 assumption of a firm structure can hardly be reconciled with 

 the principles concerned of metabolism. 



In consideration of this difficulty it seems easier to assign 

 the role of mediator of disintegration not to heat but to elec- 

 tricity. Production of electricity is likewise a property of all 

 living substance. Differences of electrical potential between two 

 points may be equalized in the stretch by conduction through 

 the intervening space. Electricity would then fulfil the impor- 

 tant conditions, which must be demanded for the form of energy, 

 acting as mediator for the conduction of disintegration from 

 cross section to cross section. 



La_t 



ROJLl 



TI 



TO—S 



Fig. 25. 



Model of a "Kemleiter." A, B— Glass tube, with a number of side tubes 

 filled with saline solution, through which a wire is passed, c and d— 

 Side tubes with electrodes for stimulation, e and f— Tubes for con- 

 nection with a galvanometer. (After Hermann.) 



Physiologists even at an early date, misled by the apparent like- 

 ness in the conduction of excitation, especially in the nerve, to 

 that of electricity in a metal wire, regarded both processes as 

 identical. When, however, Helmholtz first demonstrated experi- 

 mentally the rapidity of the conduction in the nerve, the thought 

 that electrical conduction was concerned, such as takes place in 

 a metal wire, had to be abandoned, as the velocity shows too 

 great a difference in the two cases. 



The observations, on the other hand, on the conductivity in the 

 so-called "core model," seemed to offer another possibility of 

 attributing the conduction of excitation in the nerve to electric 



