300 MUSCULAR CONTRACTION. L.ECT. XVI. 



in muscular fibres which are torn, and of which, conse- 

 quently, one at least of their extremities is free. But, 

 even according to Bowman's opinion, muscular contraction 

 must determine the locomotion of a limb, for the inac- 

 tive parts of the muscle, would be placed under the same 

 circumstances as the tendinous extremities which are de- 

 void of contractility. 



Power of Muscles at different Periods of Contraction. 

 Schwann has made some important researches on the va- 

 riations of the muscular force, according to the different 

 degrees of contraction of a muscle ; but I shall restrict 

 myself to a notice of the principal result which he obtained. 

 The force displayed during contraction, is always propor- 

 tional to the length of the muscle at the different periods 

 of contraction : so that this force, which is very great in 

 the beginning, when the contraction commences, dimi- 

 nishes in proportion to the shortening of the muscle, and 

 vanishes when the contraction has attained its maximum. 

 A muscle which contracts may, consequently, be compared 

 to an elastic thread stretched by a weight, and which, when 

 this is removed, resumes its primitive length with a force 

 invariably proportional to the weight which it supported, 

 and to the elastic -elongation it had undergone. This re- 

 sult is a refutation of the assumption, often made, that 

 muscular contraction is due to the reciprocal attraction of 

 the globules, or elementary particles which compose the 

 muscular fibre. If this were true, the force exhibited by the 

 muscle ought to augment during contraction : on the con- 

 trary, the result obtained by Schwann might be explained 

 by saying, that, contraction is produced by the instantane- 

 ous cessation of a repulsion, assumed to exist between the 

 discs, and excited the instant previously. 



Hypothesis of Muscular Contraction. I take this opportu- 

 nity of saying a few words respecting an hypothesis which 



