PHYSICO-CHEMICAL BASIS OF TRANSMISSION 383 



blance to those observed in nerve and other conducting 

 protoplasmic systems. The possibihty of transmissions 

 of the general type above is thus demonstrated, and the 

 problem becomes chiefly one of determining the special 

 nature of the conditions present in the living system. 

 It is obvious that polarization effects are present at 

 the surface of the iron wire when a current is passed 

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

 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 briefly, with more 

 particular reference to the case of nerve, where the 

 phenomena of protoplasmic transmission appear 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 element, 

 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 current at the 



