144 niYSIOLOGY OF MUSCLES AND NERVES. 



anode. If an ascendiog current is passed through a 

 nerve, the anode side is situated in its lower portion ; 

 but if the current is descending, then it is situated in 

 the upper portion. If Kitter's tetanus is induced by 

 means of a descending current, and if the nerve is bi- 

 sected between the electrodes immediately after the 

 opening of the current, the tetanus at once ceases. If 

 the same experiment is tried with an ascending current, 

 then the cutting of the nerve in no way influences the 

 tetanus. 



Yet another proof of the truth of this hypothesis is 

 afforded by Pfluger's study of the excitement of the 

 sensory nerves by an electric current. As the terminal 

 apparatus of sensory nerves, by the action of which the 

 irritation is recognised, is situated at the opposite end 

 of the nerve, it seems that the law of pulsations should 

 prevail in an opposite way to that in which it pre- 

 vails in the case of the motor nerves. Pfliiger as- 

 certained that in reality strong ascending cm'rents 

 induce sensation only when closed, strong descending 

 currents only when opened. The explanation is the 

 same in this case as in that of the motor nerves. On 

 the closing of the descending current, excitement oc- 

 curs in the lower portion of the nerve. In order to 

 effect sensation the excitement must pass to the spinal 

 marrow and the brain ; it would have, therefore, to pass 

 through the upper parts of the nerve, where it would be 

 checked by the strong anelectrotonus which prevails 

 there. The opening of the ascending current has a 

 similar irritating effect on the lower parts of the nerve. 

 In order to reach the spinal marrow and brain, this 

 excitement would have to pass through the upper parts, 

 where, in this case, it would be checked by the strong 

 negative modification. 



