300 riivsini.oiiY or Mr.-n.rs AM> NF.KVES. 



together effect a gre.iter pulsation than does a single irrita- 

 tion. 



If more than two irritants follow each other in rapid 

 succession, tetanus results, as we know. In this case also 

 the height of elevation is always greater than that which 

 ran be attained by a single pulsation. For the muscle has 

 the power of being again irritated even when it is already in 

 the act of contraction, a more powerful contraction being 

 thus induced in it. The bearing of these facts on the case 

 of nerve is that the separate excitements effected in it by 

 these rapidly successive irritations do nob mutually disturb 

 each other, but are transmitted one after the other, iu the 

 sequence in which they originate, to the muscle on vJiich 

 they act. But when the number of the irritants becomes 

 too great, the nerve-molecules are no longer able to k< ep 

 pace with the rapidly succeeding shocks, and the nerve is 

 uncxciti-d. The limit at which this intervenes has, how- 

 ever, not yet been determined with any certainty. It 

 appears to lie at between SOO to 1000 irritants per second. 



4. CURVE OF EXCITABILITY. RESISTANCE TO TRANSMISSION 



(p. 123). 



The increased excitability at the upper parts of the un- 

 injured sciatic nerve, when not se\en,l from the hod\ . 

 which, on the strength of our earlier experiments, we have 

 assumed in the text, has recently been again defended by 

 Tiegel against various objections. For reasons explained in 

 the text, it is inadmissible to infer an avalanche like incn a^- 

 in the irritation merely from this higher excitability of the 

 upper parts. 1'vside the experiments of Munk alluded to 

 on page 11G, there are other experiments from which a 

 tance to tran>nnVsion in the nerve may be inferred. 

 Such a resistance, weakening the irritant during its propa- 

 gation, and an avalanche like increase in the irritant, are 



irreconcilable contradictions which mutuallv exclude each 



