INHIBITION. 167 



of these experiments (which do not broach the question of 

 the existence of specific inhibitory nerves) seems to be that 

 as excitation may replace the quiescent by the active state 

 so also may excitation replace the active by the quiescent 

 state. The same electrical excitation causing: contraction of 

 relaxed muscle, brings about the relaxation of contracted 

 muscle (veratrinised). In this case we have to do with 

 direct excitation of muscle. In the recent observation of 

 Kaiser (and also in the older, if less precise, observations of 

 Schiff) we have to do with muscular relaxation by indirect 

 excitation — a muscle put into tonic contraction by chemical 

 excitation of its nerve (by glycerine) is made to relax by 

 tetanising induction shocks also applied to nerve. 



These are perhaps the least ambiguous data in the direc- 

 tion of the much sought for proof of the existence of muscular 

 inhibitory nerves ; they cannot be regarded as satisfactory, 

 but in comparison with other data to which appeal has been 

 made they are clearness itself. Hering's presentation of 

 anodic depression of nerve excitability as a case of inhibition, 

 Mosso's observations on human muscle, Wedensky's ex- 

 periments on frog's muscle, have very slight and distant 

 connection with the question, and are at best suggestive of 

 many various possibilities. 



To draw the conclusion that there are inhibitory nerves 

 to muscle from the fact that the electrical excitation of 

 nerve may interfere with and diminish voluntary and arti- 

 ficial muscular contractions is a step requiring considerable 

 credulity. The datum is, in fact, even more complicated by 

 possibilities than an analogous datum under more simplified 

 conditions that was brought forward by Schiff 1 forty years 

 ago, and rejected by him as fallacious evidence of musculo- 

 inhibitory nerves. The experiment is a well-nigh forgotten 

 one, and may therefore fitly be redescribed as "new ' —the 

 nerve of an ordinary nerve-muscle preparation is tetanised 

 by induction shocks until the muscle ceases to respond ; at 

 this time single induction shocks applied to another part of 

 the nerve at intervals sufficiently long to allow of recovery 



1 Schiff, Physiologic des Mcnschen, p. 188. Lahr, 1858. 



