ON NERVE-EXCITATION BY THE NERVE- CURRENT. 153 



If the sciatic nerve is cut a few millimeters above the origin of 

 its femoral branches, excitation of the nerve at the knee with the 

 above-mentioned weak currents usually gives a very weak secondary 

 effect or none at all. A similar result follows if the sciatic is cut 

 above its division into tibial and peroneal nerves, and either of 

 these is divided as far down as possible and excited at its peripheral 

 end. Perhaps this is due to the fact that at these points the 

 fibres of the branches in question have already separated from 

 the remaining fibres so as to be gathered together in separate 

 bundles, although they are contained in the same common sheath 

 with these remaining fibres. In the plexus itself the fibres which 

 are submitted to direct excitation are apparently mingled with 

 those which are to be indirectly excited, a disposition which must 

 be very favourable to secondary excitation. But besides this it 

 is possible that a greater excitability of the fibres within the 

 plexus is to be taken into account. I have sought in vain to obtain 

 secondary contraction by dipping into hot water the foot of the leg 

 of which the plexus had been just previously divided ; and I have 

 in vain suddenly frozen, or touched with a hot glass rod, the peri- 

 pheral end of a sciatic nerve which had been laid bare and cut 

 above the knee ; secondary contraction was never obtained. But 

 with crushing of the nerve I have seen a very weak and partial 

 contraction of a thigh-muscle twice and three times in succession 

 at each crushing, in two cases out of three preparations. I should 

 not like however to lay much stress upon this, seeing the large num- * 

 ber of unsuccessful experiments I have made. 



These negative results need not be surprising if one bears in 

 mind how difficult it is to produce a strong negative variation of 

 the nerve-current by non- electrical excitation, and how much more 

 certainly the secondary contraction derived from muscle itself is 

 produced, when the nerve of the primary preparation is excited 

 electrically, than when other stimuli are employed. Indeed a steady 

 and enduring tetanus can be obtained only by electrical excitation 

 of the primary nerve. 



Distinction between the true secondary contraction and the paradoxical 

 contraction of du Bois-~Reymond. 



As is well known, du Bois-Reymond observed that when a 

 sciatic nerve which had been severed from the spinal cord was 

 excited electrically, muscles supplied by branches which left the 

 nerve above the point of excitation, contracted, and that he called 



