GENERAL PHYSIOLOGY OF MUSCLE AND NERVE. 69 



effect upon the heart. 1 If the anode rest on the ventricle of the frog's heart, 

 and the kathode at some indifferent point, relaxation is seen in the region of the 

 anode with each systole of the ventricle. Inasmuch as the rest of the ventricle 

 contracts, the pressure of the blood causes the wall of the ventricle to bulge 

 out, and make a little vesicle at the region of the anode. A similar inhibitory 

 influence may be observed upon an ordinary striated muscle at the point of 

 application of the anode, if it be in a condition of tonic contraction when the 

 battery current is sent into it. During the flow of the constant current through 

 a muscle, the irritability is increased in the region of the kathode and decreased 

 in the region of the anode. When the current is withdrawn from the muscle, 

 on the other hand, the irritability of the kathode is found to be decreased, and 

 at the anode to be increased. 



Effect of the Electric Current upon Nerves. The polarizing effects of a con- 

 tinuous constant current are the same upon a nerve as upon a muscle, with the 

 exception that in the case of the nerve the condition of altered irritability is 

 not so strictly limited to the point of application of the anode and kathode, but 

 spreads thence throughout the part of the nerve between the two electrodes, the 

 intrapolar region, as it is called, and for a considerable distance into the parts 

 of the nerve through which the current does not flow, i. e. the extrapolar region. 

 The term electrotonus has been applied to the effects of battery currents on 

 nerves and muscles, and includes two sets of changes (1) physiological, mani- 

 fested by the alterations of irritability which we are considering; (2) physical, 

 exhibited in changes of the electrical condition of the tissue. The most im- 

 portant work on the influence of the constant current on the irritability of nerves 

 was done by Pfliiger. He ascertained the electrotonic effects of the polarizing 

 current to be most vigorous in the immediate vicinity of the anode and kathode, 

 and to spread thence in both directions along the nerve. He called the change 

 produced in the nerve in the region of the anode " anelectrotonic," and the 

 condition itself " anelectrotonus," while the change at the kathode was termed 

 " katelectrotonic," and the condition " katelectrotonus." The same names are 

 given to the effects of battery currents upon muscles. 



To test the effect of a constant battery current upon the irritability of a 

 nerve, put the nerve of a nerve-muscle preparation upon two non-polarizable 

 electrodes (A, K, Fig. 27) which are placed at some little distance apart and 

 at a considerable distance from the muscle. Connect these electrodes with a 

 battery, introducing into the circuit a key (&), which permits the current to 

 be quickly thrown into or removed from the nerve, and a commutator (C), 

 which allows the current to be reversed and to be sent through the nerve in 

 either the ascending or descending direction. Connect the muscle with a myo- 

 graph lever, arranged so as to record the height of the muscle contractions. 

 Then apply to the nerve at some point between the polarizing electrodes and 

 the muscle a pair of electrodes (/) connected with the secondary coil of an 

 induction apparatus, which is placed near enough to the primary coil to cause 

 excitations of medium strength, and introduce into the secondary circuit a 

 1 Biedermann : Elektrophysiologie, 1895, p. 195. 



