ANIMAL AND VEGETABLE 185 



Nor does Schafer really commit himself definitely to 

 the statement that plain muscle is not transversely striated. 

 He says : " Plain muscular tissue is composed of long, 

 somewhat flattened, fusiform cells which vary much in 

 length. 



" Each cell has an oval or rod-shaped nucleus, which 

 shows the usual intra-nuclear network, and commonly one 

 or two nucleoli. The cell -substance is finely fibrillated, 

 but does not exhibit cross-striae like those of voluntary muscle 

 There appears, as in cardiac muscle, to be a delicate non- 

 striated external layer, probably a stratum of undifferen- 

 tiated protoplasm, certainly not a true sarcolemma. . . . 

 There is a little intercellular substance which is bridged 

 across by filaments passing from cell to cell. Some 

 authorities, however, deny that the involuntary cells are 

 thus connected, and hold that the appearance of bridging 

 fibres is due to intercellular connective tissue. It is, 

 however, difficult to understand how the contractions are 

 propagated from cell to cell if there is no sort of continuity 

 between the cells." * 



Now, in regard to the speculative explanation I am 

 about to give, it is very necessary to remember that this 

 tissue responds but slowly to a stimulus, and that the 

 contraction spreads as a wave from fibre to fibre. If we 

 depart from the theory of condenser-action the problem 

 must, so far as I am concerned, remain without attempt at 

 solution, but if we adhere to it we may begin to see day- 

 light. 



These fibres of involuntary muscle are, admittedly* 

 longitudinally striated. They, however, contract and 

 become shorter and broader. It is quite evident tha* 

 with condenser-action and longitudinal striation only they 

 would merely flatten (Figs. 96; 97) : 



* The italics are mine. 



