CHAPTER IV. 



1. Alteration in elasticity during contraction ; 2. Duration of con- 

 traction ; the myograph ; 3. Determination of electric time ; 

 4. Application of this to muscular pulsation ; 5. Burden and 

 overburden muscular force ; 6. Determination of muscular 

 force in man ; 7. Alteration in muscular force during contrac- 

 tion. 



1 . We now approach one of the most remarkable of 

 the facts connected with the general physiology of the 

 muscles : this is the alteration in the elasticity of a 

 muscle during its contraction. Even E. Weber, who 

 first penetrated deeply in his researches into the sub- 

 ject of muscular contraction, showed that muscle is 

 further extended by the same weight when it is in a 

 state of activity than when it is quiescent. This is the 

 more striking because the muscle becomes shorter and 

 thicker during its activity, so that it should conse- 

 quently be less extended ; for, as we found, the exten- 

 sion by a definite weight is greater in proportion as the 

 body extended is longer, and is less in proportion as the 

 body extended is thicker. If, therefore, an active muscle 

 is further extended than one that is inactive by the same 

 weight, this can only be due to a change in its elasti- 

 city. It is hard to say how this occurs. The pheno- 

 mena of contraction may, however, be explained by 

 saying that muscle has two natural forms : one proper 



