KEACTION OF MOTOR NERVES TO DIRECT STIMULATION. 593 



Thus, in the first period, the excitability of the nerve being undiurinished, 

 contraction of the muscle takes place as soon as this molecular state of the 

 nerve undergoes alteration, which occurs both at the moment of closure and 

 of breaking of the current ; but by degrees, as the excitability of the nerve 

 diminishes, contraction takes place only on the closure of the descending 

 current, and on the opening of th{3 ascending current. But the breaking of 

 the ascending current is equivalent to the formation of a descending cur- 

 rent, that is to say, that with these two directions the muscle only contracts 

 with a descending current. In the same way, at the moment of breaking a 

 descending current an ascending current is formed which remains without 

 action on the muscles like the ascending current of the battery. At the 

 fourth period the ascending current only gives the contraction of opening 

 when the current has been applied for some time, for then the (descending) 

 polar current becomes more energetic. At the fifth period, when the cur- 

 rent of the battery no longer gives any contraction, this may still be some- 

 times obtained by the polar current. Thus Onimus maintains that by tak- 

 ing into consideration the formation of a polarizing current, and the greater 

 action of the descending current, all the phenomena of Pfluger's alternations 

 admit of ready explanation. 



The subject of electrotonus, however, must not be dismissed without a notice of 

 the work which Dr. Radcliffe has recently been doing in this direction. 1 Dr. Rad- 

 cliffe does not agree with Du Bois-Reymond, in thinking that the electrotonic move- 

 ments of the needle are to be accounted for by the nerve-current being modified by 

 the voltaic current. He questions some of the old facts, and brings forward several 

 new facts ; and he has certain explanations to offer which, to say the least, are as 

 simple as those to which attention has been already directed. 



(ft) He calls attention in the first place to certain facts which make it difficult to 

 believe that the electrotonic movements of the needle have to do, as Du Bois-Rey- 

 mond supposes, with changes in the nerve-current, produced by the action of the 

 electrotonizing current upon the nerve. 



One such fact, which is brought to light by simply going on a little further with 

 the ordinary experiments upon fresh nerves, is this, that the movements in question 

 continue/o?' a long time offer the final disappearance of tlie nerve-current. 



Another fact of like import is this, that movements of the needle in all respects 

 like those of electrotonus, are to be observed, not only when there is no nerve-current 

 in the nerve to be modified, but even when the nerve itself is taken away, and an- 

 other bad conductor used in its stead. If, for example, a piece of common hempen 



1 Dynamics of Nerve and Muscle, post 8vo. ; Macmillan & Co., 1871; Vital Mo- 

 tion a Mode of Physical Motion ; in the Press. 



