

THEORY OF THE BREAK-CONTRACTION. 55 



on application of a strong current A, must also occur with a weaker 

 current B, if only this current is closed soon enough after the 

 stronger current is opened. For, to the polarisation produced by 

 the .current B, which of itself is not sufficient to cause a break- 

 contraction, there is added the polarisation remaining over from the 

 current A, and the sum may now be strong enough to liberate a 

 contraction. Further, under such circumstances, the break-con- 

 traction must the more certainly appear, and must be the greater 

 in extent the sooner the current B is closed after the opening 

 of A. 



These phenomena are very easily observed in excitation experi- 

 ments. The description of them by Biedermann is in accordance with 

 the preceding considerations. He found in fact that ' directly after 

 a break-contraction liberated by a strong current, weak currents, pre- 

 viously only effective at make, exercise an excitatory action at break 

 which is almost as intense as that of the strong current. This excita- 

 tion-effect diminishes, however, in a short time, and disappears completely 

 after a few minutes of rest if the nerve is sufficiently vigorous. More- 

 over, under conditions otherwise the same, this peculiar effect is the more 

 persistent the greater the period of lime during which the stronger current 

 has operated, and the less active the nerve is V 



The full parallelism between the break-contraction and polarisa- 

 tion may be very elegantly demonstrated with one and the 

 same strength of current on an ordinary nerve-muscle prepara- 

 tion. I performed such experiments in this way. I passed a 

 current of a given strength through the nerve for periods of 

 various duration. If the period was very short, only a make-contrac- 

 tion occurred ; if it was longer, there was also a break-contraction. 

 If, directly after the break-contraction appeared, I again closed 

 the current and opened it again very soon, repeating the experiment 

 in this way for several successive times, I obtained a whole series of 

 break- contractions, which by-and-bye fell off in size, and at last 

 quite ceased, to reappear as soon as I allowed the current to act on 

 the nerve for a longer time. In these experiments therefore there 

 appeared in the break-contractions all the phenomena which I had 

 previously become acquainted with by means of the galvanometer. 

 In order to throw more light on the question I shall here com- 

 municate some examples of experiments. 



In the following records, T 1 = the duration of the closures ; 



1 Biedermann, Wiener Sitzungsberichte Math. Part iii. vol. 83, p. 328, 1881. 



