AFTER ELECTRICAL STIMULATION. 273 



It must be remembered that du Bois-Reymond was then of 

 opinion that the electrical current excited the nerve in an equal 

 manner throughout the whole, of the tract through which it flowed. 

 Since however Pfiiiger's original researches on Electrotonus, we know 

 that the current has polar actions which are quite different at the 

 anode from what they are at the kathode. And when du Bois-Rey- 

 mond, in his researches on secondary electromotive phenomena in 

 nerve and muscle, still maintains an equal internal (positive and 

 negative) polarisation for the whole of the intrapolar tract, he is 

 in my opinion in error. The so-called secondary electromotive 

 phenomena are the consequence of polar actions, and like the 

 excitability exhibit a polar difference. Thus it happens that elec- 

 tricity flowing unipolarly through the galvanometer electrodes into 

 the circuit of the multiplier, appreciably alters the nerve in their 

 neighbourhood, and there completely changes its electromotive 

 behaviour ; hence the alterations in the nerve current which occur 

 during and after stimulation are in no wise solely the result of the 

 general alteration of the nerve. 



Where du Bois-Reymond discusses the influence of the strength 

 of the stimulating current on the amount of negative variation, he 

 says (vol. ii. p. 451) expressly : ' In this case the use of the induction- 

 coil has no disadvantages.' And yet it is just here, where strong 

 stimulating currents have to be dealt with, that unipolar action is 

 most to be feared. 



Thus it is sufficiently evident that du Bois-Reymond's state- 

 ments differ in many respects from what we learn from the investi- 

 gation of negative variation when unipolar actions are excluded. 

 I will not here examine how far the above described behaviour of 

 the nerve current on stimulation with strong induction currents, 

 depends on unipolar action and thus on direct stimulation and 

 alteration of the galvanometer tract, or how far it depends only on 

 an increase of excitation propagated from the stimulated to the 

 galvanometer tract. I would only add this, that with vigorous 

 nerves and with methods of excitation which exclude unipolar 

 actions, I never succeeded in observing such behaviour of the nerve 

 current during stimulation as was shown when strong induction 

 currents were used and unipolar actions in consequence obviously 

 came into play. 



I will not enter on a theoretical discussion of the positive after- 

 variation until I have described some other electrical phenomena in 

 stimulated nerves. 



