MUSCLE. 349 



scribed, yet it would not be safe to adopt the conclusion 

 from this, that they represent the several stages of the 

 normal contraction of a muscular fibre. Again, it might be 

 argued, that the nodular condition described as belonging 

 to a muscle in a state of active contraction would be most 

 unfavourable for the full exercise of the power of contrac- 

 tion, seeing that the nodules of one fibre would necessarily 

 interfere with those of the contiguous fibres, and thus im- 

 pede its own as well as their contraction. 



For the above reasons, therefore, I would place but little 

 reliance upon the experiment quoted, and prefer to adopt an 

 explanation more simple in its character, and yet entirely 

 sufficient to explain the condition of a muscle during its state 

 of most active yet entirely normal contraction. 



I conceive that no distinct line of demarcation exists 

 whereby active and passive muscular contraction can be dis- 

 criminated : the two are but different degrees of the same 

 power, and manifest themselves by phenomena which differ 

 not in kind, but simply in extent. 



If a muscle of the leg of a frog be isolated from its fel- 

 lows, or if the tongue of the same animal be extended and 

 pinned to the margins of an aperture made in a piece of 

 cork, the only change which can be observed to take place 

 in the muscular fibre, when stimulated to contraction, consists 

 in an approximation of its stria?, neither waves nor nodules 

 manifesting themselves in its course. 



Again ; immersion of muscular fibre, which has almost lost 

 its contractile power in water, will be followed by an ap- 

 proximation of the striae, and a proportionate increase in the 

 diameter of the filament. 



Now, the approximation of the stria? is the only visible 

 sign which I have ever been able to detect in natural mus- 

 cular contraction ; and it is amply sufficient to account for 

 the shortening and increase in diameter which a muscle un- 

 dergoes during its state of most active contraction. 



The distance between the stria? in a fibre placed somewhat 

 on the stretch, as are all muscular fibres in their natural 

 state, and in that which is in a state of contraction, varies 



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