STRIATED MUSCULAR FIBRE. 



199 



Fig. 101. 



$; 

 ^iliifii-... 



-j 





siderable traction is being exercised, there is continual interchange in the ele- 

 ments by which it is effected, the discs at one end of the contracted part 

 receding from each other, whilst at the other end new discs are being re- 

 ceived into it. 



232. The foregoing description is chiefly 

 derived from the appearances presented by 

 muscular fibre, when spontaneously passing 

 into that state of contraction, which is termed 

 the rigor mortis ; but there can be no rea- 

 sonable doubt, that the phenomena of con- 

 traction, excited by the agency of the nerves, 

 are precisely similar. Mr. Bowman has re- 

 marked, that stimuli of various kinds, direct- 

 ly applied to them, produce corresponding 

 effects, although, in the case of galvanism, 

 the change is too rapid for its steps to be 

 followed ; and that, from the appearances 

 presented by muscles which have been af- 

 fected with tetanic spasms, the contraction 

 produced by nervous agency may be inferred 

 to correspond in character. It now remains, 

 therefore, to inquire what is the cause of the 

 zig-zag arrangement, which is often seen in 

 the fibres. This may be easily produced, by 

 approximating the ends of a fasciculus, after 

 the irritability of its fibres has ceased ; and 

 it would not seem unlikely, that the passage 

 of vessels or nerves should determine the 

 points at which the flexures take place. 

 Hence it appears, that the sinuous or zig-zag 

 arrangement is that into which fibres are 

 naturally thrown, if, on elongation following 



contraction, they are not at once stretched by antagonist muscles.* Many 

 facts support the opinion, which has long been held by several Physiologists, 

 that, when an entire muscle is contracting, all its fasciculi are not in con- 

 traction at once ; but that there is a continual interchange in the parts, 

 by which the tension is effected ; some relaxing, whilst others are short- 

 ening. When the ear is applied to a muscle in vigorous action, an exceed- 

 ingly rapid faint silvery vibration is heard; which seems to be attributable to 

 this constant movement in its substance. Now, on examining a muscle, of 

 which some fasciculi present the zig-zag arrangement, others will be seen (if 

 the two extremities have not been purposely approximated) to be quite straight, 

 and in a state of contraction ; and it thence appears, that the former appear- 

 ance is presented by bundles of fibres, which have either not yet entered into 

 contraction, or which have relaxed after undergoing it; but of which the ex- 

 tremities are still approximated, by the agency of other contracting fibres. 

 The result of various experiments made for the purpose, leads to the conclu- 

 sion, that the total bulk of a muscle in contraction is not less than when it is 

 in a relaxed state ; or that the difference, if any exist, is extremely trifling. 



233. Every Muscular Fibre, of the striated kind at least, is attached at its 

 extremities to white fibrous tissue ; through the medium of which it exerts its 

 contractile power on the bone or other substance, which it is destined to move. 



Muscular fibre of Skate,'in a state of 

 rest (1), and in three different stages of 

 contraction (2, 3, 4). , 



* Mr. Bowman's conclusions have recently been confirmed by Prof. E. Weber. (Archives 

 d'Anatomie Generale, Jan. 1846.) 



