EFFECT OF BATTERY CURRENTS ON DEEP-SEATED NERVES 537 



During the passage of a constant current through a nerve and immediately 

 after its cessation, there is a change in the conductivity as well as of the irri- 

 tability of the nerve at the anode and cathode, respectively. During the pas- 

 sage of the current, the conductivity is increased at the cathode and decreased 

 at the anode. After the passage of the current, the effect is reversed. With 

 strong currents the area of decreased conductivity may be sufficient to act as a 

 block, preventing the passage of impulses over it. 



The foregoing statements concerning the changes produced in a nerve 

 by the passage of a constant current may be briefly summarized as follows: 



I. A nerve is more irritable to the closing of a constant current than it is to 

 the opening of a constant current. 



II. During the passage of the current through the nerve, both its irritability 

 and conductivity are increased at the cathode and decreased at the anode. 



III. After the passage of the current, the irritability and conductivity are 

 both decreased at the cathode and increased at the anode. 



The Effect of Battery Currents on Deep-seated Nerves. The follow- 

 ing account is condensed from Lombard in "An American Text-book of 

 Physiology." 



As an electric current cannot be applied to living human nerves directly, 

 it is applied to the skin along the course of the nerve. The current passes 



Skin 



FIG. 33 50. Diagram of Skin and Subjacent Nerve. A, the positive electrode or 

 phvsical anode; B, the negative electrode or physical cathode. Signs, -f- physiological 

 anodes; signs physiological cathodes. (After Waller.) 



from the anode or positive pole through the skin, and spreads out in the 

 tissues much as the bristles of a brush; it then gradually concentrates and 

 leaves the skin at the cathode or negative pole. 



In addition to the physical anode and cathode of the battery, there are 

 what are called physiological anodes and cathodes. There is a physiological 

 anode at every point where the current enters a nerve, and a physiological 

 cathode at every point where it leaves it. 



Generally when the current is applied to nerves through the skin, only 

 part of it flows longitudinally along the nerves; most of it passes diagonally 

 across them to the tissues below. Thus it happens that in that part of the 

 nerve beneath either the physical anode or cathode, groups of physiological 

 anodes and cathodes are found. 



The contraction which occurs when the current is closed (closing con- 

 traction) represents irritation at the physiological cathode, while the opening 



