178 



PHYSIOLOGY OF MUSCLES AND NERVES. 



The case of organic tissues, with which we are con- 

 cerned, is of the latter sort ; for we have seen that 

 when these are inserted between the ends of a homo- 

 geneous arch, electric action takes place under certain 

 circumstances. The fact that in other cases no such 

 action occurs will be intelligible after the account just 

 given, for we may assume that in such cases the two 

 points which are touched by the ends of the arch are 

 similar in tension. 



Let BODE (fig. 44) represent a section through 



E —^ — ^~ — I D 



+ 



/" 



I'lG. 44. CURRENT-CUKVES AND TENSION-( U IIVES. 



a body in which an electromotive force is present. For 

 the sake of simplicity we will assume that the body 

 is a regular cylinder, and that the electromotive force 

 is situated in its axis ; then that which we show in 

 the case of B G D E will be equally true of every 

 other section. Let the point A represent the seat of 

 electromotive force ^ which sets the positive electricity 

 in motion toward the right, the negative electricity 

 toward the left. The whole body is then occupied by 



* In order to have a phj-sical basis for this electromotive force we 

 may imagine the cylinder to consist of a fluid, and that at the point 

 A is situated a body consisting half of zinc, half of copper. 



