96 INTRODUCTION. 



current will be weakened by the counter current; in a third 

 reduced to zero ; and in a fourth reversed. To these assumptions 

 no one, I anticipate, will make any objection. I shall assume 

 nothing more ; for they are amply sufficient to render the pheno- 

 mena which I observed, and my explanation of them intelligible. 



Two additional points seem worthy of separate consideration. It 

 might perhaps be objected that, since so many currents of different 

 directions and strengths and taking different paths are passing in 

 the nerve, it is impossible to say anything definite at all as to their 

 effects. It would be necessary to suppose that the effects of the 

 incompletely, the completely, and the over-compensated currents 

 would manifest themselves simultaneously. This would be the case 

 if all the fibres in the sciatic nerve were motor fibres of the gastro- 

 cnemius in which we are studying the effects of excitation. The 

 motor fibres however form, if the sensory and other fibres in the 

 sciatic are taken into consideration, perhaps a twelfth of all the 

 fibres, according to a rough calculation. It is only, therefore, what 

 occurs in that twelfth and its immediate neighbourhood that is of 

 importance to us. The current-changes occurring in the remain- 

 ing eleven-twelfths have no significance for us, or practically 

 none. When, therefore, in the one above-mentioned twelfth of a 

 nerve trunk the diminished nerve-current mounts at break of the 

 counter-current to its original height, we have the break-con- 

 tractions before the hiatus ; when the nerve-current is exactly com- 

 pensated, the hiatus ; when it is over-compensated, the contractions 

 after the hiatus. 



Hermann 1 says, in connection with the subject of compensation 

 of nerve-currents : ' It might be thought possible to do away, with 

 the demarcation-current altogether by over-compensating. This 

 is, however, entirely impossible, since the lines of flow of the 

 counter-current in the nerve run quite differently from those of the 

 demarcation-current. Internal compensation is thus inconceivable, 

 and the less so the nearer the proper electro-motive surface. The 

 enormously strong currents in the immediate neighbourhood of the 

 latter will be little affected by external currents ever so strong 

 although these produce a special polarisation in the nerve.' I have 

 nothing to object to this, nor does it contradict what I have said j 

 for, as already mentioned, it is not necessary to my explanation of 

 the hiatus that the demarcation-current should be entirely abolished. 



1 Pfliiger's Archiv, xxx. p. 15. 



