88 CONTRACTILE ELEMENTS. 



only, in this incomplete return, that the zigzag form is 

 observed. 



Two theories now contend for the explanation of this phe- 

 nomenon. 



According to some (Weber, Aeby, Marey), the almost 

 liquid contents of the muscular fibre are the 'seat of a series 

 of waves (muscular wave), whose presence produces the 

 shortening of the muscle, and its transverse enlargement. 



According to others (Rouget), the muscular fibres are 

 decomposed into smaller and very numerous ^fo^Ys, formed 

 by a sort of spiral line. As the juxtaposition of these spiral 

 lines explains the striated appearance of the muscular fibre, 

 so their lengthening or shortening gives us the key to the 

 first and the second form, and to that caused by the passage 

 from one to the other. 



Marey has shown that if two of those myographical pincers, 

 which are used to register the swelling which takes place in a 

 muscle when contracted, be placed at a certain distance from 

 each other lengthwise upon the muscle, these two pincers will 

 not record the swelling of the muscle at the same instant ; the 

 one nearest the extremity which is excited acts first, and then 

 the other. The swelling of the muscle thus advances like 

 a wave, of which the velocity has been estimated by Marey 

 at one metre a second. Aeby has, however, shown that if, 

 instead of exciting the muscle at one extremity only, it be 

 excited throughout, by placing each extremity in contact 

 with one of the wires of the exciting current, or if the motor 

 nerve of the muscle be excited ; the two tracings made by 

 the myographical pincers are exactly superposed or syn- 

 chronic. In this case the muscular fibre contracts in all its 

 parts at once. 



Professor Rouget has observed, by examination of the 

 contractile pedicle of the vorticelli, that the muscular fibre 

 is a true spiral spring (p. 68), which, actively distended during 

 the repose of the muscle, returns upon itself at the moment 

 of contraction: muscular contractility is a purely physical 

 property of elasticity ; the rigidity of a corpse is a phenom- 

 enon of the same order as muscular contraction in the living 

 body. " The stem of the vorticella presents the principal 

 organ of locomotion of an animal, formed by a single muscular 

 fibril, free in a tube, at the centre of a perfectly transparent 

 sheath; which allows us to see with the greatest distinctness 

 all the changes undergone by the contractile element during 

 its state of activity or of repose, of elongation or of con- 



