THEOKY OF THE BREAK-CONTRACTION. 69 



tractions occur, is easily explained by my theory. Since the current 

 can with the greatest ease branch off into all possible paths, its 

 density in the nerve is so small that the polarisation cannot attain 

 sufficient strength to liberate a contraction. This is possible only 

 if very strong currents are used (Brenner J ). 



The experiments of Claude Bernard, Schiff, and Valentin, which 

 are often cited in proof of the absence of a break-contraction on 

 stimulation of living nerves, will not bear close examination. It is 

 impossible to obtain exact results if, like Valentin, we insert 

 electrodes directly into the thigh of an animal without dissection; 

 the branch of the current which reaches the nerve with such a pro- 

 ceeding must always be very small 2 . The strength of the current 

 employed by Claude Bernard, or rather by Rousseau, who performed 

 the experiments in question, is nowhere given 3 . Chauveau confirms 

 Claude Bernard's results, but adds that, when stronger currents are 

 used, the break-contraction makes its appearance. 



As to the strength of his currents Chauveau also says nothing ; 

 he merely assures us that the break-contraction appears with currents 

 which do not alter the normal properties of nerve 4 ; how the absence 

 of the break-contraction in uninjured nerves can be deduced from 

 this, I cannot conceive. Schiff too says nothing as to the arrange- 

 ment of his experiments and the strengths of current which he 

 used. 



His assertions, therefore, cannot stand as evidence for the absence 

 of break-contractions with uninjured nerves, the more so as he says 

 himself that his law in general holds ' if the duration of the current 

 is not too prolonged ; ' he subsequently admits that ' with consider- 

 ably increased strengths of current ' the second or third degree of 

 contraction may be ' evoked with living nerves V 



' Living nerves,' according to Schiff, are therefore not quite in- 

 sensible to the break-stimulus. The contrast between ' living ' and 



1 Hermann, Handbuch der Physiologie, i. p. 63, 1879. 



2 Valentin, Die Zuckungsgesetze des lebenden Nerven und Muskels, Leipzig und 

 Heidelberg, 1863. 



3 Claude Bernard, Lecons sur la Physiologie et la Pathologic du Systems nerveux, 

 i. Paris, 1858, p. 185. 



* Chauveau, Journal de la Physiologie, No. x, April, 1860, p. 283. 'It is certain 

 that the passage of currents through motor nerves in the normal condition provokes 

 contractions only at the moment of closing, whether the currents are ascending or 

 descending. But it must be understood that we are using batteries sufficiently weak ; 

 otherwise the double contraction manifests itself even with the currents which are far 

 from being sufficiently strong to alter the properties of the nerve and when the physio- 

 logical conditions leave nothing to be desired.' 



6 Schiif, Lehrbuch der Physiologie des Menschen, i. pp. 80, 81, 1858-9. 



