ANIMAL AND VEGETABLE 145 



elastic, sheath insulation ; the whole being so arranged as 

 to be capable of neuro-electrical contraction in almost 

 every direction. The chain of condensers might, indeed, 

 contract more suddenly, or violently, at one point than at 

 another point or points, but the various contractions would 

 be designed to give, under impulse, a certain definite 

 movement or series of movements to the muscle under 

 excitation. 



I now learn from Landois and Stirling's Text-book 

 of Human Physiology that each muscular fibre receives 

 a nerve-fibre, or wire from a central station or 

 stations. 



The elastic sheath is called sarcolemma, and has 

 transverse partitions stretching across the fibre at regular 

 intervals. Within the sarcolemma is the contractile 

 substance of the muscle. This, sarcous, substance is 

 marked transversely by alternate light and dim layers, 

 stripes, or discs. 



These muscular compartments contain the sarcous 

 substance, and in each compartment there is a broad dim 

 disc, forming the contractile, or compressible, part, on the 

 upper surface, as shown in the illustration (p. 147) ; then, 

 lower down, a narrower, " clear," homogeneous, soft or fluid 

 substance ; then a membrane (called Krause's membrane), 

 and another clear substance, followed by a dim (com- 

 pressible) disc, and so on throughout the fibre. 



Let us imagine the sarcolemma to be composed of 

 india-rubber, at all events on its inner side, the dim 

 substance to be an elastic buffer, the " clear " lines to be 

 conducting plates or discs, and Krause's membranes or 

 Dobie's lines to be dielectric in character, and condenser 

 action is suggested, once it is conceded that the impulse is 

 neuro-electrical. It is not a question, as I have argued in 

 another chapter, of whether the impulse is neuro-electrical 

 or chemical, but of which action is precedent. 



L 



