ELECTKOTONTJS. 115 



ological writers to Pfaff. 1 After a time, varying with the 

 excitability of the nerve and the intensity of the current, the 

 direct current will destroy the nervous irritability, but this 

 may be restored by repose, or more quickly by the passage 

 of an inverse current. If the inverse current be passed first 

 for a few seconds, a contraction follows the breaking of the 

 circuit ; and this contraction, within certain limits, is more 

 vigorous the longer the current is passed. At the same time, 

 the prolonged passage of the inverse current increases the 

 excitability of the nerve for any kind of stimulus. When 

 the inverse current has been passed through the nerves for 

 several hours, breaking of the circuit is followed by very 

 violent contraction and a tetanic condition of the muscles, 

 enduring for several seconds. 



Electrotorvus, Anelectrotonus, and Catelectrdtonus. 



Many years ago, Du Bois-Keymond discovered the curious 

 and interesting fact, that when a constant galvanic current 

 is passed through a portion of a freshly-prepared nerve, those 

 parts of the nerve not included between the poles are brought 

 into a peculiar condition. While in this state, the nerve 

 will deflect the needle of a delicate galvanometer and its ex- 

 citability is modified. 9 The deflection of the needle, in this 

 instance, is not due to the normal nerve-current, for it occurs 

 when the galvanometer is applied to the surface of the nerve 

 only. It is due to an electric tension of the entire nerve, in- 

 duced by the passage of a current through a portion of its 

 extent. This condition is called electrotonus. The phe- 

 nomena thus produced have been most elaborately studied by 

 Pfliiger, who further recognized a peculiar condition of that 

 portion of the nerve near the anode, or positive pole, differing 

 from the condition of the nerve near the cathode, or negative 

 pole. 2s ear the anode,'the excitability of the nerve is dimin- 



1 LONGET, Traite de physiologic, Paris, 1869, tome iii., p. 194. 

 8 Du BOIS-REYMOND, Utitersuchungen uber thierische Elektricitat, Berlin, 1849, 

 Bd ii., S. 289, et seq. 



