MUSCLES OF ANIMAL LIFE. 



277 





Muscular fibre of Skate, in a state of 

 rest (1), and in three different stages of 

 contraction (2, 3, 4). After Bowman. 



of the fibre thus tend to approximate -is Fig. 67. 



evidently considerable ; for if the two ex- 

 tremities be held apart, the fibre is not 

 unfrequently ruptured. This corresponds 

 with the appearances found in the muscles 

 of persons who have died from tetanus ; 

 for in the ruptured fibres of those muscles, 

 which had been the subjects of the spas- 

 modic action, the striae have been observed 

 to approximate so closely as to be scarcely 

 distinguishable. When the contraction is 

 not very decided, the dark and elevated 

 spot appears to play like a wave along the 

 fibre, before it involves the whole diameter 

 in any part ; and even when considerable 

 traction is being exercised, there is con- 

 tinual interchange in the elements by 

 which it is effected, the disks at one end 

 of the contracted part receding from each 

 other, whilst at the other end new disks 

 are being received into it. 



372. The foregoing description is chiefly 

 derived from the appearances- presented by 

 muscular fibre, when spontaneously pass- 

 ing into that state of contraction which is 

 termed the rigor mortis ; and it has not 

 been fully demonstrated that the pheno- 

 mena of contraction, excited by the agency 

 of the nerves, are precisely similar. Mr. Bowman has remarked, however, that 

 stimuli of various kinds, directly 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 affected 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 zigzag 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 zigzag 

 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 physi- 

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

 contraction at once ; but that there is a continual interchange in the parts by 

 which the tension is effected ; some relaxing, whilst others are shortening. 

 When the ear is applied to a muscle in vigorous action, an exceedingly 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 zigzag arrangement, others will be seen (if the two ex- 

 tremities have not been purposely approximated) to be quite straight, and in 

 a state of contraction ; and it thence appears, that the former appearance is 

 presented by bundles of fibres, which have either not yet entered into con- 

 traction, or which have relaxed after undergoing it, but of which the extremi- 

 ties are still approximated by the agency of other contracting fibres. From 

 the fact that a single muscular fibre, isolated from all other tissues, can pass 

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