ANIMAL AND VEGETABLE 



187 



layer must be elastic to permit contraction and that 

 they should be bridged at intervals by some non-conducting 

 substance, possibly connective tissue. Condenser-action 

 would then take place as in voluntary tissue, and the rate 

 of propagation of the impulse would be governed by the 

 considerations set forth in the chapter upon Inductive 

 Capacity. 



In this manner we can perceive how the contraction 

 spreads as a wave from fibre to fibre, and why it is that the 

 cells vary much in length. They also, no doubt, vary much 

 in diameter in order to enable the tension to be varied, 

 but there is this essential difference, I think, between 

 voluntary and plain muscle : the former is required to 

 contract in curves, at different velocities in the course of 

 those curves and not in the same direction throughout, 

 while the function of the latter is merely to shorten. 



If that is so a less complicated form of fibre would serve 

 the purpose, nor would the complex end-organ connec- 

 tions be necessary. We cannot compare the cells, for 

 reasons I have given, to a chain of condensers in series, 



i.e. J^~\ | j | 1 j 1 1-2^-, but must imagine them 



to be connected in parallel or series-parallel. Nor is 

 this opinion without warrant, as the following figure goes 

 to show : 



Fig. 100. MUSCLE-CELLS OF INTESTINE (SZYMONOWICZ), MAGNIFIED 

 530 DIAMETERS. (After SchAfer.) 



