62 AN AMERICA X TEXT- BOOK OF PHYSIOLOGY. 



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 When the current is withdrawn from the muscle, 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) manifested by the 

 alterations of irritability which we are considering; (2) exhibited in changes 

 of the electrical condition of the tissue. 



There can be little doubt that both of these sets of changes are the result 

 of electrolytic alterations of the nerve protoplasm, caused by the flow of the 

 polarizing current. We shall consider here only the former of these sets of 

 changes. The true nature of the electrotonic changes of the electrical condi- 

 tion of the nerve, and their relation to the nerve impulse, embrace a number 

 of difficult problems, which are still under discussion and cannot be profit- 

 ably considered here. 1 



The most important work on the influence of the constant current on the 

 irritability of nerves was done by Pfliiger. 2 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 " an electrotonus ;" while the 

 change at the kathode was termed " katclectrotonic," and the condition 

 " katelectrotonus." The same names are given to the effects of battery cur- 

 rents 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. 29) 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 quicklv thrown into or removed from the nerve, and a commutator (O), 

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



1 Waller: Lectures on Animal Electricity, London, 1897; Biedermann: Eleclrophysiology, 

 translated by F. A. Welby, 1898, rol. Li. 



'' Pfliiger: Untermchwngcn iiber die Physiologic des Electrotonus, Berlin, 1859. 



