LECT. XII. XIII. REFLEX MOVEMENTS. 229 



Two Periods in the Action of the Current on the 

 Nerves. We must, therefore, divide into two different pe- 

 riods the action of the electric current on the nerves of a 

 living animal. In the first, the irritation of the nerve is 

 transmitted in all directions towards its central part, as well 

 as to its periphery, both at the commencement and cessa- 

 tion of its action, and independently of the direction of the 

 current. In the second period, the excitation of the nerve 

 is transmitted towards its periphery, during the first mo- 

 ments of the action of the direct current, and at the instant 

 of the interruption of the inverse current : on the contrary, 

 when the direct current is interrupted, or when the circuit 

 of the inverse one is being closed, the irritation of the nerve 

 is transmitted towards the brain. 



I may express the whole of these results in more simple 

 terms : the current acts in the direction in which it is trans- 

 mitted, when it begins to circulate in the nerve, and in the 

 opposite direction when it ceases to circulate. 



Before we proceed further, we must inquire how the 

 electric current can occasion contractions of the muscles of 

 the back and of the head, by acting, as we have seen in 

 the preceding experiments, on nerves which are not dis- 

 tributed to them. 



If you divide the spinal marrow of a rabbit transversely, 

 and cause an electric current to pass along the crural nerve, 

 you will observe that the contractions are, in this case, con- 

 fined to the muscles situated below the point where the 

 spinal marrow was divided ; and if this was effected near 

 its inferior extremity, no contractions will occur in the 

 muscles situated above the excited nerve. 



Reflex Movements. The contractions excited in the 

 muscles situated above the irritated nerve by an electric 

 current, are then reflex movements. The excitation of this 

 nerve is transmitted to the spinal marrow, and the latter, 



