353 



the current, for the lumbar nerves on this side are traversed by an 

 inverse derived current ; and this, as the Table shows, is actually 

 the case. 



A similar diagram and table will show that the results of passing a 

 direct primitive current through a portion of the lumbar nerves on 

 one side are in accordance with the same law. In this case, as in 

 the other, the acting current on both sides is the derived current. 

 On the side acted upon by the direct primitive current, the acting 

 derived current (acting because nearest to the muscles supplied by 

 the nerve) is inverse ; and therefore the limb on this side ought to 

 contract at the end of the current. On the opposite side, the course 

 of the derived current is direct, and therefore the limb on that side 

 ought to contract when the current begins to pass : and so it is. 



Fig. 2. 



The results of the action of a galvanic current upon a loop of 

 sciatic nerve are, after a time, analogous to those which have just 

 been mentioned. At first, the contraction attending upon the 

 beginning and ending of both currents affects the whole limb ; after 

 a time, the leg and thigh contract alternately, in an order which 

 changes with the direction of the current. 



Let the following diagram and table represent the case in which a 

 loop of sciatic nerve is acted upon by the direct primitive current, 

 a being the nerve, P N the poles of the galvanic apparatus, the black 

 arrow the primitive current, the dotted arrows the derived current ; 

 and it will be seen that the portion of nerve between the negative 



