206 STUDIES IN ELECTRO-PHYSIOLOGY: 



To the electrician the construction of a multipolar cell 

 to transmit efferent and afferent impulses would be a 

 comparatively simple matter. Take two hollow metal 



globes or ellipses or modifications 

 ^ e i tner > place one inside the 

 other in such manner that there 

 is an air-space or insulating layer 

 between them, and drill a hole in 

 the outer globe to receive an 

 Fig. ill. insulated wire, which would make 



metallic contact with the inner 



globe (Fig. 111). The next step would be to solder a 

 number of insulated wires to the outer globe, and to then 

 provide absolute insulation for the whole by coating the 

 outer globe with, say, gutta-percha solution or Chatterton's 

 compound. 



Now, in a Ley den jar the inner and outer coatings are 

 metallic, the glass walls of the jar form the dielectric 

 substance, and discharge is prevented by the resistance 

 interposed by air intervening between the outer coating and 

 the earth. In the human body all the nerves are to earth, 

 through the air, and the resistance of that intervening 

 stratum of air is sufficiently great to prevent discharge, 

 under normal conditions of charge, taking place prematurely. 

 When, however, a motor or secretory nerve receives an 

 efferent impulse, or it may be impulses, the added tension 

 is just enough to bridge the spark gap, as it were, and so to 

 permit of a discharge or partial discharge. 



It will be seen, however, that the surface area and 

 therefore the tension of the two globes, as sketched in 

 Fig. Ill, is not the same, and that if the impulse conveyed 

 by the axon were an efferent impulse all the wires connected 

 to the outer globe would transmit lower-tension afferent 

 impulses, in which case the cell would not be multipolar. 

 But in the majority at least of these cells there are 



