CH. XI.] 



EXTENSIBILITY OF MUSCLE. 



CHAPTER XI. 



EXTENSIBILITY, ELASTICITY, AND WORK OF MUSCLE. 



MUSCLE is both extensible and elastic. It is stretched by a 

 weight, thai is, it possesses extensibility ; when the weight is 

 Laken off, it returns to its original length, that is, it possesses 

 elasticity. The two properties do not necessarily go together; 

 thus a piece of putty is very extensible, but it is not elastic ; 



Elastic Band 



Muscle 



fig. 154. (After Waller.) 



a piece of steel or a ball of ivory are only slightly extensible, but 

 after the stretching force has been removed they return to their 

 original size and shape very perfectly. 



A substance is said to be strongly elastic, when it offers a great 

 resistance to external forces : steel and ivory are strongly elastic. 



A substance is said to be perfectly elastic, when its retuni to 

 its original shape is absolute ; again steel and ivory may be 

 quoted as examples. 



Muscle is very extensible, i.e., it is easily stretched ; it is feebly 

 elastic, i.e., it opposes no great resistance to external force ; it 

 is, however, perfectly elastic ; that is, it returns to its originnl 

 shape very exactly after stretching. This is true in the case of 

 living muscle within the body, but after very great stretching 



K 2 



