ANIMAL AND VEGETABLE 169 



dielectric process offering resistance, and therefore inter- 

 posing delay to the passage of the current or impulse. 



Halliburton has told us, and it is an important fact 

 to remember, that each nerve-unit is anatomically inde- 

 pendent of every other nerve-unit. The arborisations 

 interlace and intermingle, and nerve impulses are trans- 

 mitted from one nerve-unit to another, through contiguous, 

 but not through continuous structures. Furthermore it is 

 open to question whether a so-called continuous current 

 of electricity is continuous in the strictest sense of the 

 word, or whether it is really a series of polarisations and 

 discharges occurring with such velocity as to. appear to be 

 continuous. 



Put shortly, the views taken of the propagation of 

 electric force by molecular action consider the molecules of 

 the interpolar wire to be as follows : 



Fig. 89. 



c being the copper and z the zinc end, the shaded parts 

 being -f and the unshaded . The first effect of the 

 electric force developed by the chemical affinity of the 

 zinc for the O or S(L is to throw all the molecules of the 

 circuit into a polar condition, the force being transmitted 

 from molecule to molecule in both directions. Positive and 

 negative electricities appear in each molecule of the 

 circuit ; and if the action be powerful enough, discharge 

 takes place throughout the whole, each molecule giving out 

 its electricities to those next it, which, throwing out the 

 opposite electricities, produce electric quiescence through- 

 out. A constant series of such polarisations and dis- 

 charges, taking place with enormous rapidity, constitute 

 a current. 



In the body the impulse may be, and probably is, 



