OBSERVATIONS ON STRIPED AND UNSTRIPED MUSCLE. 101 



works, the latter being in direct connection with the nerve. 

 It is therefore difficult to conceive that the transverse net- 

 works can contract actively after the longitudinal bars have 

 begun to relax, for the nervous impulse will apparently reach 

 the former first, and hence they must contract at the same time 

 as or before the longitudinal bars ; and yet if the relaxation of 

 the fibre is held to be due to active contraction of the trans- 

 verse networks this is what must occur. 



Conclusion. 



The conclusion to which I am therefore led is that the con- 

 traction of the striped muscle-fibre is due to the active con- 

 traction of the longitudinal bars of the network, and that the 

 transverse networks are probably passively elastic, and by their 

 rebound cause relaxation of the muscle-fibre. That the 

 transverse networks and the muscle-corpuscles, with which 

 they are said to be continuous, possibly furnish paths by which 

 the nervous impulse is conveyed from the nerve ending to the 

 longitudinal bars. That the contraction of the unstriped 

 muscle-fibre is due to the active contraction of its longitudinal 

 fibrils when these are present (as in vertebrate muscle). In 

 the case of unstriped muscle which possesses no fibrils the 

 contraction is due to the whole protoplasm of the cell, there 

 being no special part differentiated to perform this function. 



Should these conclusions prove to be correct, we may 

 imagine the changes that occur in the striped muscle-fibre 

 during contraction to be as follows : 



The nervous impulse reaching the end-plate of the nerve is 

 conducted by the transverse networks to the longitudinal bars, 

 and causes them to shorten ; it does not cause the transverse 

 networks to contract, because they are passively elastic and 

 non-contractile. The longitudinal bars shorten according to 

 the strength of the nervous impulse, and remain so as long as 

 it lasts. By fluid pressure the transverse networks are ex- 

 tended and remain so as long as the longitudinal bars remain 

 contracted ; when these cease to contract the elasticity of the 



