ELECTRICAL BREAK-EXCITATION. 



119 



strength of the polarisation-current at its first appearance as com- 

 pared with the strength of the original current. Is the strength 

 of the former equal to, smaller, or greater than that of the latter ? 

 I am unfortunately not in a position to give any definite reply to 

 this question. If, however, we reflect that a nerve is an organ 

 which possesses in a high degree the capability of being polarised, 

 if further we call to mind the relative values which du Bois-Hey- 

 mond 1 and others 2 have found for the strengths of the original 

 and polarisation-currents, it will not seem too high a value if we 

 assume that the polarisation-current is equal in strength to the 

 original current. 



If, however, this question must for the present be left un- 

 answered, there is a second question which can be decided by 

 experiment. This second question is: To what fraction of its 

 original strength must an exciting current fall in order that an 

 excitation of a nerve and muscle, a so-called ' incomplete ' break- 

 contraction, may occur? The way in which this question may 

 be settled is simple. It is only necessary to arrange a mercury 

 key A (see Fig.) in the course of the 

 wire of the compensator D2/ and 

 best close to the point D, where the 

 current divides. A second mercury 

 key C is placed in the main circuit 

 UD'B. If the main circuit is closed at 

 C while the derivation-circuit is open, 

 the whole current from the battery 

 passes through the nerve ; and if 

 the key A in the derivation-circuit 

 is now closed also, the current falls 

 to a certain fraction of its strength, 

 which fraction is of course the 

 smaller the smaller the distance be- 

 tween D and E" . The current 

 strength could thus be altered from 8 to any strength between 

 o and f S. 



The most remarkable fact which we observed was that the 

 direction of the original current has a most important influence 

 on the appearance of imperfect break-contractions. It was found 

 as mean of a large number of experiments that an ascending 

 current of the strength of one Daniell, which was of course led 



1 Ges. Abhandlungen, i. p. 43. 2 See Wiedemann, Electijcitatslehre. 



Fig. I. Main or battery circuit 

 BCD'D. Derivations or nerve cir- 

 cuit Dee, D". 



