EFFECT OF BATTERY CURRENTS ON DEEP-SEATED NERVES 473 



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 irrita- 

 bility 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 

 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 through 



Shin 



FIG. 335 A. Diagram of Skin and Subjacent Nerve. A, the positive electrode or physical 

 anode; B, the negative electrode or physical cathode. Signs, + physiological anodes; signs- 

 physiological cathodes. (After Waller.) 



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 

 contraction represents irritation at the physiological anode. Since there are 

 physiological anodes and cathodes beneath each electrode, one or more of 

 four conditions may arise: 



i. Anodic closing contraction, i.e., the effect of the change developed at 

 the physiological cathode, beneath the physical anode (positive pole). 



