2/8 COMPARATIVE ELECTRO-PHYSIOLOGY 



more important, moreover, is the disturbing factor last 

 mentioned, that of the inequality of excitatory values as 

 between the make- and break-shocks themselves. This 

 element of uncertainty is very clearly seen in the experi- 

 ments of Von Fleischl on the response of nerve. The 

 resulting deflection he found to be in the direction of the 

 break-shock. The explanation of this phenomenon has 

 hitherto been regarded as a matter of great difficulty, 

 authorities being much divided on the subject. In these 

 experiments, alternating currents from a Ruhmkorff's coil 

 are sent through the galvanometer and the nerve, in series. 

 The two points on the nerve, A and B, are presumably of 

 equal excitability. A make-shock of relatively lower E.M.F. 

 passes, say, from A to B, followed by a break-shock of higher 

 E.M.F. in the opposite direction, from B to A. Confining 

 our attention to the excitatory effects of these shocks, we 

 have at A, during make and break, the following four effects : 

 (a) feeble anode-make ; (b) feeble anode-break ; (c) strong 

 kathode-make ; and (d) strong kathode-break. At B, on the 

 other hand, at the same time, we shall have : (a') feeble 

 kathode-make ; (b r ) feeble kathode-break ; (c'} strong anode- 

 make ; and (d'} strong anode-break. Now, since the excitatory 

 value of anode-break is probably the stronger and more 

 persistent, and since the intensity of this effect will depend, 

 within certain limits, on the intensity of the anodic shock, it 

 follows that the (d') or strong anode-break effect at B will, as 

 a general rule, be the most conspicuous of these. That is to 

 say, as a result of all these excitatory effects in combination, 

 greater galvanometric negativity will be induced at B than at 

 A, the responsive current being thus from B-*A, in the same 

 direction as the break shock, which was the actual result. In 

 any case, whatever may have been the cause of this, it is 

 clear that the employment of such unequally exciting shocks 

 of make and break would be fatal to any attempt to 

 determine accurately the natural difference of excitability as 

 between the two points. I may state here, that when I have 

 employed absolutely equal alternating shocks on a specimen 



