72 CONTRIBUTION TO THE 



than the nerve-current, or of the same strength, there will be no make- 

 contraction, but this will appear whenever the stimulation-current 

 is the stronger of the two. If the exciting current is weaker than the 

 nerve-current the result is the same as if a weak ascending current 

 flowed through the nerve during the whole period of closure ; at the 

 moment the exciting current is opened the nerve-current suddenly 

 attains its full strength. Its negative pole now coincides with a part 

 of the nerve which is in a state of heightened excitability due to the 

 previous descending current. Through this rise of excitability the 

 break-excitation becomes sufficiently strong to evoke a muscular 

 contraction. If the stimulating current is of the same strength 

 as the nerve-current, the latter is neutralized ; when the stimulating 

 current is broken the nerve- current appears in its full strength. 

 Now, however, there is no part of the nerve endowed with a 

 heightened excitability, and the break-stimulus by itself is too weak 

 to generate a contraction. If the polarising current is still further 

 strengthened, it overpowers the nerve-current and produces a 

 polarisation, which, in conjunction with the nerve-current flowing 

 in the same direction, calls forth a break-contraction. 



Griitzner's idea that the break-contraction which appears first is 

 due to the nerve-current seems completely proved by the pheno- 

 menon of the ' gap ' (Liicke) which he observed in his series of 

 break-contractions. That the break-contractions occurring after 

 the ' gap,' as to the origin of which Griitzner has not expressed an 

 opinion, do not owe their appearance to the nerve-current, is evident 

 without discussion if we only bear in mind the actual conditions. 

 But it is very easy to see why, after the gap, the break-contractions 

 become stronger and stronger, for they are due to the polarisation- 

 current, the strength of which increases with that of the exciting 

 current. 



Let us now suppose that a descending current is led through a 

 divided nerve in the neighbourhood of the cut surface. This current 

 must evoke a contraction even when of very weak strength, since 

 it is added to the nerve-current flowing in the same direction. (For 

 proofs of this see Griitzner's papers above quoted, pp. 163, 167.) If 

 the strength of the stimulating current is gradually increased, the 

 contractions increase correspondingly to a maximum, and, as might 

 be anticipated, no gap presents itself. When the current is broken, 

 the polarisation-current flows in a direction opposed to that of the 

 nerve-current. We can in this case, therefore, obtain a break- 

 contraction only when the polarisation-current has become stronger 



