TEXT-BOOK OF PHYSIOLOGY 



Cohesion. The cohesion of a muscle is largely dependent on the quan- 

 tity of connective tissue it contains. A band of fresh human muscle i 

 square centimeter in cross-section has been found able to resist a weight of 

 14 kilograms without rupture (MacAlister). Cohesion resists the forces of 

 tractipn and pressure. 



Elasticity. Muscle, in common with many other organic as well as 



inorganic substances, is capable of being ex- 

 tended beyond its normal length by the action 

 of external forces and of resuming the normal 

 length when these forces cease to act. All such 

 bodies are said to be elastic; and the greater the 

 variations between the natural and acquired 

 lengths, the greater is their elasticity said to 

 be. Muscles, therefore, possessing extensibility 

 and retractility are said to be elastic. If the 

 muscle of a frog, preferably the sartorius, the 

 fibers of which are arranged in a practically 

 parallel manner, be fastened at one extremity 

 by a clamp, and then extended by a series of 

 successive weights which differ by a common 

 increment, it will be found that the extensi- 

 bility of muscle does not follow the law of 

 FIG. '18. EXTENSION CURVE OF elasticity as determined for inorganic bodies; 

 MUSCLE. (Gad.) i.e. , directly proportional to the weight and to the 



length of the body extended; but that while in- 

 creasing in length with each successive weight, the increase is always in a 

 diminishing ratio. Thus, for example, as shown in Fig. 18: The exten- 

 sion produced by 5 grams is 5 millimeters, that produced by 10 grams is 

 only 4 millimeters more, and so on with additional weights until the in- 

 crease in passing from 25 to 30 grams is only i millimeter. The exten- 

 sibility is thus shown to be proportionately 

 greater with small than with larger weights. It 

 is, however, actually greater with the larger 

 weights. The extension curve A B formed by 

 joining the ends of the muscle approximates that 

 of a parabola. The behavior of 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 gradu- 

 ally increasing energy until its normal length is 

 nearly, if not entirely, regained (Fig. 19). It is sion. (Landois an 

 usually stated that the elasticity of muscle is in- 

 complete, but it must be borne in mind that the experiments have usually 

 been made on muscles removed from the body, deprived of blood and 

 nerve influences, and hence under abnormal conditions. It is highly prob- 

 able that in the living body muscles possess perfect elasticity which enables 

 them completely to return to their normal length after extension. The 

 extension and retraction or elastic recoil of muscle depends on the main- 

 tenance of physiologic conditions. If the nutrition is impaired by fatigue, 



FIG. 19. CURVE OF ELAS- 

 TICITY PRODUCED BY CONTINU- 

 OUS EXTENSION AND RECOIL 



