The Demarcation Current of Mammalian Nerve. 325 



" The Demarcation Current of Mammalian Nerve. (Preliminary 

 Communication.) III. The Demarcation Source and ' the 

 Concentration Law.' " By J. S. MACDONALD, B.A., L.E.C.P.E., 

 University College, Liverpool, Eesearch Scholar of the British 

 Medical Association. Communicated by Professor SHERKIXG- 

 TON, F.K.S. Eeceived October 18, 1900. 



Since writing the previous statement the changes of E.M.F. occurring 

 during the early part of the time spent in saline solutions have been 

 studied more in detail, the nerves being removed every five minutes for 

 examination. 



As a result of information so acquired, the following statement can 

 be definitely made. Solutions of NaOH, HC1, NaCl, KC1 mainly 

 affect the demonstrable value of the demarcation source according to 

 their concentration, and differ intrinsically from one another in their 

 effects upon this source only in minor characteristics. 



Each of these electrolytes produces an effect which is best regarded 

 as a variation of the effect of water, and varies with the concentration 

 according to a simple law. The concentration in each case determines 

 whether the initial value of the demonstrable E.M.F. shall be increased, 

 maintained, or diminished. 



A study of the comparative effects of various concentrations of the 

 same electrolyte is of particular interest when the nerve is only 

 immersed for a short period (five minutes), presumably because within 

 this period processes of diffusion interfere least with the concentration 

 of electrolytes in the internal parts of the nerve. 



The concentration law found to unite the effects of solutions of 

 NaCl, KC1, HC1 is comparatively simple, the case of solutions of NaOH 

 being apparently more complex. 



If " E " represents the initial value of the E.M.F., 



"E n " the value after an immersion of 5' duration in a solution of 

 concentration " n," 



" n " the concentration in gramme-molecules per litre, 



then in the special case of solutions of KC1 



E n = Elog- approximately. 



'/& 



Thus, taking the data from four experiments performed upon 5 cm. 

 pieces of sciatic nerves (cat), determining the available E.M.F. between 

 cross section and longitudinal surface (a) immediately upon removal 

 from the recently killed animal, and (I) after an immersion of 5' in a 

 solution of KCl at 17 C. : 



VOL. Lxvn. 2 15 



