112 THE NATURE OF THE 



published it. Thus there are wanting- in Hermann's investigations 

 the exceedingly important control experiments to determine whether 

 the excitation at break of the primary current is due entirely or 

 principally to the polarisation-current. He might quite as well have 

 been dealing with apparent, additive break-contractions due to the 

 appearance of the nerve-current. To judge from my own experience, 

 it is exceedingly probable that such might have been the case, since 

 as a rule the electrodes are so applied to a nerve that nerve-currents 

 pass through them. The earlier appearance of break-contractions 

 with descending currents, which Hermann records, appears to me 

 to point to additive break-contractions being also included in these 

 experiments (at least very often), or to the nerve- and polarisa- 

 tion-current having passed simultaneously through the derivation- 

 circuit. 



In addition to this, the break-contractions before may be con- 

 founded with those after the hiatus, if the hiatus is short and does not 

 appear at the same point when the main circuit is broken as when 

 the nerve-circuit is broken. The fact that differences, even of a 

 tenth of a second, in the duration of closure of the primary current 

 affect the appearance of break-contractions very considerably should 

 also be mentioned. I myself was once misled by this source of error 

 through the one mercury key being less easy to manage than the 

 other and so keeping the current closed a little longer. Finally, in 

 comparative experiments the current ought not to be changed from 

 a higher to a lower strength, and the long persistence of the 

 polarisation-current must be kept in mind. All this is of importance 

 for the attainment of accurate results. Although I by no means 

 believe that Hermann neglected these facts and so fell into error, 

 yet I am convinced that in his experiments the nerve- and polarisa- 

 tion-current have been intermingled, or have acted simultaneously. 

 Otherwise he would not, if I may so say, have written so hesi- 

 tatingly : * When the break-contraction is struggling for exist- 

 ence it appears, if there is any difference at all,' &c. What I 

 described was not a struggle : in a' very large number of ex- 

 periments, which I have considerably increased since the appear- 

 ance of Hermann's paper, the break-contraction appeared much 

 sooner after opening the main circuit than after opening the 

 nerve-circuit. 



The difference becomes much greater (as is seen in the experi- 

 ments at page 108) if ordinary metallic electrodes are substituted for 

 unpolarisable electrodes. The internal and external polarisation- 



