108 CONTRACTILE ELEMENTS. 



the leg. Indeed, the inferior limb represents, in oscillat- 

 ing, a double pendulum (the thigh on one side, the whole of 

 the limb on the other). It is well known that the law of 

 oscillation in a pendulum is that a pendulum composed 

 of two parts united by a joint bends slightly in the joint as 

 soon as it begins to swing. 



Some physiologists, however, deny that the leg which we 

 have called passive is entirely passive ; they maintain that it 

 undergoes a slight degree of contraction of the flexors, pre- 

 cisely in order to produce the flexion necessary to the oscil- 

 latory movement. Duchenne (of Boulogne) draws, from 

 his pathological observations, the conclusion that the oscil- 

 latory motion of the leg would be impossible, without the 

 contraction of the flexors of the thigh upon the pelvis, of 

 the flexors of the leg upon the thigh, and of the flexors of 

 the foot upon the leg. 1 It is difficult to decide on this sub- 

 ject, for some authors here bring in the question of muscular 

 tonicity, and that of the predominance of the flexors over the 

 extensors. On these questions we have already given our 

 opinion (see p. 72). 



Some important modifications are to be observed in the 

 movements made in walking, according as they take place 

 on level ground, or in going up and down a staircase, for 

 instance ; and these have been carefully analyzed by Marey 

 ("Journal de 1* Anatomic," 1873). We cannot pursue the 

 subject further here, but will only give the essential features 

 of running, as mentioned by this physiologist. In running 

 there is no double support, but, on the contrary, a time of 

 suspension, during which the body remains for a moment 

 lifted above the ground, one foot having just left it, and the 

 other not having yet touched it. The length of this time 

 of suspension appears absolutely to vary very little ; but if 

 it be compared with the length of a step in running, we find 

 that the relative value of the suspension increases with the 

 speed of the running, because, as this increases, the length 

 of time during which the foot remains on the ground is 

 diminished. What is most remarkable, however, is the 

 means by which, according to Marey, this interval of suspen- 

 sion is produced: we might at first suppose it to be the 

 effect of a sort of leap, by which the body is thrown upwards, 



1 Duchenne (de Boulogne), " Physiologic des Mouvements." 

 Paris, 1867, p. 386. 



