THE TISSUES 



55 



Increasing the strength of the stimulus shortens the latent 

 period, but lengthens the periods of contraction and relaxation. 



6. Resistance to Contraction Weight to be Lifted. Start- 

 ing from the extent of muscular contraction without any load 

 it is found that small weights attached to the muscle actually 

 increase the extent of contraction, but that greater weights 



St. 



Con. 



A3 c 



FIG. 25. Influence of increasing the Strength of the Stimulus upon the con- 

 traction of Skeletal Muscle. St., the stimulus ; Con., the resulting 

 contraction. A, a subminimal stimulus ; B, the minimum adequate 

 stimulus ; C, the optimum stimulus. 



diminish it, until finally, when a sufficient weight is applied, 

 the muscle no longer contracts at all, but may actually slightly 

 lengthen, because its extensibility is increased during contraction 

 (fig. 26, a). 



The application of weights to a muscle causes the latent 

 period and period of contraction to be delayed, while it renders 



Flo. 26. Influence of Load on a Muscular Contraction, (a) The effect of in- 

 creasing the load on the extent of contraction ; (b) the effect of load on 

 the course of contraction. 



the period of relaxation more rapid, and an over-extension may 

 be produced followed by a recovery resembling a small after- 

 contraction (fig. 26, b). (Practical Physiology.) 



7. Eleetpotonus. As already explained, the passage of a 

 galvanic current through a muscle decreases its contractility 

 at the anode and increases it at the kathode. 



