ELECTROTO2OJS. 121 



upon the action of a rapidly-interrupted current applied to 

 an excitable nerve. If a galvanometer be applied to a liv- 

 ing nerve so as to indicate by its deviation the normal, or 

 tranquil nerve-current, a rapidly-interrupted current of elec- 

 tricity passed through a portion of the nerve, it is well 

 known, produces a tetanic condition of the muscles. If we 

 now watch the needle of the galvanometer, it will be ob- 

 served to retrograde, and will finally return to zero,, indi- 

 cating that the proper nerve-current has been overcome. 

 This will be observed to a slight degree under the influence 

 of mechanical or chemical stimulation of the nerve, the 

 proper nerve-current being diminished, but generally not 

 abolished. This variation of the needle under the influence 

 of the tetanic condition has been called negative variation. 1 

 We do not yet know that it has any important physiological 

 or pathological significance. 



1 Du BOIS-REYMOXD, Untersuchungen uber thierische Ekktridtat, Berlin, 1849, 

 Bd. il, S. 425, et seq. 



