160 ELECTRO- PHYSIOLOGY CHAP. 



a process set up by these reagents, before they have had time to 

 affect the muscle-substance itself, the proof being that the lateral 

 contraction corresponding with the nerve -end plate appears 

 immediately before the death of the fibres implicated. Generally 

 speaking, all that has been said of the development of the " fixed " 

 waves applies to the origin of the lateral waves also. 



Summing up the preceding observations, the main con- 

 clusion is that the cross-striated muscle-fibres of vertebrates, 

 as well as of invertebrates, possess the faculty of conducting 

 long and short, rapidly and slowly transmitted, waves of 

 contraction, which apparently depend upon differences of excita- 

 tion only. With regard to the normal function of muscles as 

 locomotor organs, the short waves can have but little, if any, signi- 

 ficance. This only makes them theoretically the more interesting. 

 The enormous differences in rate of transmission render it at first 

 sight questionable, whether we are really dealing in both cases 

 with the same elements of the muscle-fibres, since no perceptible 

 differences in velocity of conduction have experimentally been 

 found to correspond with the differences of intensity within the 

 range of excitation required to provoke a twitch ; nor can the 

 "quick" and "sluggish" muscle-fibres contribute to the explanation, 

 since the differences which they exhibit in rapidity of contraction 

 and conductivity are quite inadequate to explain the disparity. 

 On the other hand, we turn almost involuntarily to the two 

 chief constituents of every muscle-fibre, sarcoplasm and fibrils. 

 We know that in many instances the protoplasm (sarcoplasma) 

 from which the twitching fibrils have been differentiated, is not 

 wholly wanting in intrinsic contractility ; many ciliated Infusoria, 

 e.g., have the property through the myoideum, not only of twitch- 

 ing, but also, by contraction of the body-plasma, of making sluggish 

 movements, approximating to the amoeboid type. The possibility 

 that the formative plasma of the muscle-fibres in higher animals 

 also may exhibit contractility can the less be doubted, since on 

 many sides (Kiihne) the fibrils are regarded as passive, elastic 

 elements, whose main function is the elongation of the muscle. 

 Even if this extreme view cannot be admitted to correspond with 

 the facts, it is equally out of the question to disregard the possi- 

 bility of contractility in the sarcoplasm. Granting this, however, 

 it would appear from all analogies that the relations between 

 excitability and conductivity in the two elementary constituents 



