CHAPTER LXII 

 THE CONTRACTION OF MUSCLE 



THE great property of muscle is its power of contractility. When 

 a, muscle contracts 



1. It undergoes a change in shape, becoming shorter, tenser, and 

 thicker. 



2. It becomes, as we have seen, more elastic and more extensile. 



3. It develops heat. 



4. It undergoes an alteration in its electrical condition. 



5. It suffers metabolic changes, which alter its chemical condition. 



FIG. 272. THE CRANK LEVER, MUSCLE BOARD, AND STAND. 



The Change in Form. The change in form of a muscle, when it 

 contracts, is usually registered by means of the graphic method. The 

 muscle most frequently employed for this purpose is the gastroc- 

 nemius muscle of the frog. The muscle is connected to a magnifying 

 lever, or myograph. It may either be pinned out on a board in a 

 form of apparatus resembling Fig. 272, or it may be clamped in the 

 apparatus shown in Fig. 273. The writing lever, which should be as 

 light as possible, is then made to write upon a smoked drum, or kymo- 

 graph. In order to study the time occupied by the contraction, a 



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