ELECTRICAL CURRENTS OF THE NERVES. 



585 



arranged ; but, generally speaking, increasing both with the length and with 

 the thickiK^s of the nerve. Ranke 1 has also shown that the lactic acid gen- 

 erated in nerve and muscle consequent upon the active discharge of function, 

 suffices to abolish and even reverse the ordinary nerve current, which is 

 again restored when the acid is neutralized by an alkali. In the nerves the 

 axis-cylinder, and in muscle the intermediate substance is the seat of the 

 most active chemical changes, and becomes acid ; the doubly refracting 

 muscle substance, and the doubly refracting substance of Schwann remain 

 alkaline. Ranke holds that at the point where a stimulus is applied to a 

 nerve, an increased metamorphosis takes place, accompanied by the forma- 

 tion of lactic acid, which causes regular variation of the muscle current, and 

 a state of increased irritability in the nerves. Hermann is at issue with Du 

 Bois-Reymond on several points. He contends 2 that in perfectly uninjured 

 animals the muscles, when at rest, are absolutely destitute of any current, 

 and that all currents that can be made manifest are due to injury inflicted 

 on the tissue, leading to its more rapid oxidation at the point injured, fol- 

 lowed by death. This part then becomes negative to the remainder of the 

 nerve. This view has been sharply criticized by E. Du Bois-Reyrnoud and 

 Munk. We have now to follow M. Du Bois-Reymond through his investi- 

 gations on the change in the condition of the " nervous current," whilst the 

 nerve is in a state of functional activity, whether motor or sensory. 



473. Eledrotonus of Du Bois-Reymond. Electronus is the alteration pro- 

 duced in the electromotor condition of the whole of the nerve by the passage of 

 a constant current from a battery through part of it. If a portion of nerve- 

 trunk be so placed (Fig. 196), that it touches one of the electrodes by its 



FIG. 197. 



L_-,J 



p z 



transverse section (which may be designated T), and the other by its surface 

 or longitudinal section (L), and a portion of its continuation be included in 

 a galvauic circuit, so that a current shall pass in the direction z p, which 

 is the same in its direction as that between T L, then the intensity of the 

 "nervous current" T L, as indicated by the deflection of the needle of the 

 galvanometer, will be found to undergo an increase; whilst on the other 

 hand, if the electric current be passed in a contrary direction P z, the in- 

 tensity of the "nervous current" T L will decrease. The portion z p of 

 the nerve, which is included in the electric circuit, is termed the excited por- 

 tion, and the current passed through it is the exciting current; on the other 

 hand, the portion T L included between the electrodes of the galvanometer 



Physiologic, 1872, p. 667. 



38 



2 Ibid., 1874, p. 249. 



