264 ELECTRO-PHYSIOLOGY CHAP. 



which is lower and more extended than the first phase (1), and, 

 moreover, reaches its maximum at a different point from the 

 maximum of excitation at the second lead-off. The superficies of 

 the parts of the curve corresponding with the two phases must 

 he equal ; hence their action upon the galvanometer ceases 

 simultaneously in tetanus." 



In muscle, we have in the physiological rheoscope and its 

 secondary excitation an exceedingly convenient indicator of the 

 discontinuous nature of the negative variation of the demarcation 

 current, as well as of the action current in the uninjured and 

 intrinsically isoelectric muscle. Du Bois-Eeymond tried in vain 

 to obtain secondary excitation from one nerve to another, and 

 later experimenters were no more fortunate, so that it seemed 

 impossible to decide from one excitable nerve whether another 

 was or was not excited. This is contrary to what we should 

 have expected a priori ; for the electrical variation in nerve is, 

 absolutely and relatively, a more vigorous process than that in 

 the muscle, and there is no sufficient reason why (to all appear- 

 ance) no nerve has an excitatory action upon another superposed 

 upon it. Hering (11) has now, indeed, established the possibility 

 of true secondary excitation from nerve to nerve, by availing 

 himself of every advantage, the increased excitability in the 

 vicinity of an artificial transverse section included. If the 

 peripheral end of an excitable sciatic (exposed from, vertebral 

 column to knee, and cut at both ends) of a cooled frog is applied 

 to the central end of a second nerve still connected with the leg, 

 so that the two nerves lie together for 50 mm., and their 

 cross -sections are in the same place, then the demarcation 

 current of the one nerve will, as it were, compensate that of 

 the second. " Supposing the longitudinal - transverse current 

 suddenly to disappear from the peripheral end of the primary 

 nerve (through negative variation to zero) in consequence of an 

 instantaneous excitation, the compensation of current in the 

 second nerve will be abruptly abolished. The end of the 

 primary nerve that in consequence becomes isoelectric, now 

 functions solely as a shunt to the current of the secondary nerve, 

 and the latter will be weakly excited by the sudden short- 

 circuiting of its own current. But if the direction of current in 

 the exciting nerve is reversed, it will after reversal act upon the 

 second nerve like a weak descending current, and summates with 



