86 



PHYSIOLOGY 



CHAP. 



investigations. He found that muscle has a low but perfect 

 elasticity ; it can be readily extended by small weights, but 

 promptly returns, under normal conditions, to its initial length, 

 when the extending force ceases to act on it. He recognised 

 that, unlike inorganic, but like certain organic substances, the 

 elongation of the muscle is not proportional to the weight, and 

 becomes less so as the load increases ; so that the curve of extensi- 

 bility obtained when the weights are plotted on the abscissae, 

 and the elongations taken as ordinates, is not a straight line but 

 a curve, which Wertheim subsequently recognised as a hyberbola. 

 Weber compared the elasticity of the resting hyoglossus 

 muscle of the frog with that of the same frog 'when tetanised, by 



m 



FIG. 61. Diagram to show elasticity of muscle in rest and in activity. A B, length of unloaded 

 resting muscle ; A b, same muscle in activity. A' B', A" B", length of resting muscle loaded 

 with regularly increasing weights ; A' b', A" b", length reached by active muscle loaded with 

 same weights. The line B B' B" . . . y x gives the elasticity curve of resting, b If b" . . . y, of 

 contracting muscle. 



comparing the curves of extensibility to regularly increasing 

 weights during rest and in tetanus. He found that the active 

 muscle is less elastic, i.e. more extensible than the inactive 

 (Fig. 61). '^Therefore the extensibility curve of active muscle 

 falls more rapidly than that of resting muscle. With progressive 

 increase of load a point is reached at which the two curves meet. 

 This happens when the weight is sufficiently great to hinder 

 contraction, i.e. when the elastic tension in the muscle due to 

 the weight is in complete equilibrium with the opposite elastic 

 tension which is actively set up by the stimulus. If, after 

 reaching this point, the muscle is further overloaded and then 

 stimulated, there will not only be no contraction, but, on the 

 contrary, a certain degree of elongation due to the decrease in 

 muscular elasticity after stimulation, so that the elasticity curve 

 of the active state crosses the elasticity curve of the resting state 

 (Weber). But this has not been confirmed by later workers, who 



