PHYSICO-CHEMICAL BASIS OF TRAXSMISSION 383 



blance to those observed in ncr\e and ollu-r condiutinK 

 protoplasmic systems. The possibility of transmissions 

 of the general type above is thus demonstratcfl. and the 

 problem becomes chiefly one of determinin<r the spcdal 

 nature of the conditions present in the li\ing system. 

 It is obvious that polarization elTccts are ])rcscnt at 

 the surface of the iron wire when a current is passc<i 

 through the system, just as in the case of the phitinum 

 wire in the core-conductor experiments of Hermann, 

 Matteucci, and Boruttau. Changes of polarization, 

 however, can give rise to unlimited transmission only 

 in so far as they form the condition of chemical effects 

 which alter the electromotor properties of the surface 

 layer and themselves cause further changes of polariza- 

 tion. The general conditions of transmission in proto- 

 plasmic systems will now be discussed brietly, with more 

 particular reference to the case of ners'e, where the 

 phenomena of protoplasmic transmission a])])car to 

 exhibit themselves under the simplest conditions. The 

 fundamental problem, however, is the same for all forms 

 of protoplasm. 



According to the law of polar stimulation, the direc- 

 tion of the current between active and resting areas is 

 such, relatively to the surface of the irritable clement, 

 that its normal physiological effects— assuming them to 

 be the same as those of an external current led into the 

 tissue — would be to initiate excitation at the resting 

 region adjoining the excited area and to repress activity 

 in the excited area itself. An inspection of the diagram 

 (Fig. 4) will show this. The direction of the local bio- 

 electric current (relatively to the protoplasmic surface) 

 at R is the same as that of the external currmt at the 



