PROPAGATION OF PHYSIOLOGICAL CHANGE 493 



central conductor. Before committing ourselves to any dogma 

 it is necessary to have studied the character of the core. We 

 must, in fact, find data upon which to consider the possibility 

 that the nervous impulse is no isolated phenomenon, but one 

 that has its analogue in the conveyance of excitation from point 

 to point within all kinds of cell structures where insulation 

 is neither discoverable nor theoretically required. Boruttau has 

 appreciated this necessity. He has transferred the facts of the 

 core-model to the central core. But for this transference he has, 

 in my opinion, no warrant. If the core of the individual nerve- 

 fibre does really possess a structural arrangement similar to that 

 of the core-model composed of its several parts, that fact has 

 yet to be demonstrated. The facts elicited so far are of a 

 different order. Boruttau has, so to speak, abandoned a con- 

 sideration of the sheath without omitting the very important 

 facts for which this structure is responsible from the experi- 

 mental data made use of to present the case in this new sheathless 

 form. On this, and on other grounds also, we for the time being 

 fight shy of this core-model theory of nerve function. 



Do considerations such as this, then, drive us back into the 

 arms of the biogen molecules ? Certainly not at present, since 

 the needful factors seem at least in great part physical. The 

 core has still to be studied as a conductor of electricity, that is 

 to say, as a solution of electrolytes. What are the electrolytes 

 of nerve ? How are they distributed within the nerve-fibre ? 

 How is the motion of electrolytes which takes place within 

 the core during the conduction of a nervous impulse to be 

 explained ? 



Now if at first sight it seems absurd to treat of this core, 

 this strip of protoplasm which is responsible for so much, as 

 a solution of electrolytes, let us remember our treatment of the 

 case of the cells in the sweat-gland and in the salivary gland. 

 In putting nerve material in such a category we do nothing new 

 or unexpected. This criterion " solution " is one to which every 

 cell has to be compared, and from it much information illumi- 

 nating the basis of function has already been obtained. The 

 general considerations which entail this treatment are present 

 in nerve as elsewhere. Thus the core exerts an osmotic pressure 

 upon the surfaces inclosing it, and this pressure is normally 

 balanced by the pressure of the solutions outside. Alter the 

 character of these solutions ever so little and this is at once seen. 



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