CHAP. VII.] MUSCULAR ACTION. 177 



ever minute the fragment may happen to be. This is all that can 

 be said in general of the visible features of this remarkable phe- 

 nomenon. Late investigations, instead of explaining the manner 

 in which contraction is effected, by shewing its dependence on 

 forces previously understood, have only served to display the in- 

 adequacy of the coarse and mechanical hypothesis that physiologists 

 have been so pione to confide in, and to make it more than pro- 

 bable that they must ever be content to repose upon the fact above 

 stated, as the simplest which the most refined microscopical analysis 

 will ever disclose. 



All muscle retains its contractility for a longer or shorter period 

 after its separation from the body, or after death. During this 

 period contractions may be excited by the nervous, and all other 

 stimuli, which we can apply to it ; and it is certain that these con- 

 tractions are the same in their nature with those occurring in the 

 living body under natural influences. Being also easy of inspection, 

 they are admirably suited to the display of the minute changes 

 occurring in muscle during its active state. 



The muscle with striped fibres is peculiarly adapted for the dis- 

 play of these changes ; for, its texture not being homogeneous, but 

 marked throughout with perfect regularity into spaces of particles 

 so minute as to require to be very highly magnified before they can 

 be even seen at all, the anatomist is provided with the means of 

 detecting movements, which, without this circumstance, must have 

 remained concealed. 



When a piece, retaining its contractility, is torn up into its 

 elementary fibres, the fragments of these, when placed in water, are 

 seen to undergo a slow movement at certain points, especially where 

 they have suffered violence, as at their broken extremities. This 

 movement consists of a shortening and thickening of the material 

 composing the fibre, as is shewn by the general outline of the part, 

 but especially by the appearances visible in its interior. The trans- 

 verse stripes, both light and dark, become longer and thinner : in 

 other words, the discs expand in circumference, flatten, and ap- 

 proximate to one another ; or, to use another form of expression, 

 the fibrillae become shorter and thicker, both in the particles com- 

 posing them and the material connecting those particles (fig. 49). 



These changes are always local or partial ; and it is most evident 

 from the characters they constantly present, that they are not 

 limited to any determinate regions, points, or segments, but occur 

 indifferently wherever the exciting cause may chance to be exerted. 

 Neither discs nor fibrillse appear to have the smallest share, as 



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