GENERAL PHYSIOLOGY OF MUSCLE-TISSUE. 



69 



57 



FIG. 19. EXTENSION CURVE 

 OF MUSCLE. (Gad.) 



weights until the increase in passing from 25 to 30 grams is only i 

 millimeter. The extensibility is thus shown to be proportionately 

 greater with small than with larger weights. It is, however, actually 

 greater with the larger weights. The ex- 

 tention curve A B formed by joining the 

 ends of the muscle approximates that of a 

 parabola. The muscle in returning to its 

 original length also shows a variation from 

 the behavior of inorganic bodies. With 

 the successive removal of the weights, the 

 elasticity of the muscle asserts itself with 

 gradually increasing energy until its nor- 

 mal length is nearly, if not entirely, re- 

 gained (Fig. 20). Though it is usually 

 stated that the elasticity of muscle is in- 

 complete, it must be borne in mind that 

 the experiments have usually been made 

 on muscles removed from the body, de- 

 prived of blood and nerve influences, 

 and hence under abnormal conditions. 

 It is highly probable that in the living 

 body muscles possess perfect elasticity 

 which enables them to completely return 

 to their normal length after extension. The extension and elastic 

 recoil of muscle depends on the maintenance of physiologic condi- 

 tions./ If the nutrition is impaired by fatigue, deficient blood-sup- 

 ply, or any pathologic condition, the elasticity is at once impaired. 



Tonicity. This is-- a property pos 

 sessed by all muscles in the body in con- 

 sequence of being stretched to a slight 

 extent beyond their normal length/^This 

 may be due to the action of antagonistic 

 muscles or to their mode of growth, the 

 muscles growing somewhat more slowly 

 than the bones to which they are at- 

 tached ^That muscles are so stretched 

 is shown by the shortening which at once 

 takes place when their tendons are di- 

 vided. This muscle tonus or tension is 

 closely connected with the elasticity and 



plays an important role in muscle contraction; being always on the 

 stretch, the muscle loses no time in acquiring that degree of tension 

 necessary to immediate action on the bone to which it is attached. 

 The working power of a muscle is also increased by the presence, 

 within limits, of some resistance to the act of contraction. Accord- 



FIG. 20. CURVE or ELAS- 

 TICITY PRODUCED BY 

 CONTINUOUS EXTENSION 

 AND RECOIL OF A FROG'S 

 MUSCLE, o x. Abscissa 

 before; x f , after extension. 



