114 



ANIMAL MECHANISM. 



served for the investigation of the muscular wave (fig. 7, 

 page 87). If we substitute in this figure an experimental 

 shoe for each of the myographical clips 1 and 2, we shall 

 have the arrangement of the apparatus necessary for the study 

 ot footsteps or impacts of the foot on the ground. 



Fig. 20 has been furnished by an experiment in walking. 

 Two tracings are given by the intermittent pressure of the 

 feet on the ground. The full line D corresponds with the 

 right foot ; the dotted line with the left. 



Fig. 20. — Tracings of the impact and the rise of the two feet in our ordinary walk. 



Knowing the arrangement of the apparatus, we can under- 

 stand that each impact of the foot on the ground will be 

 represented by the elevated part of the corresponding curve. 

 In fact, the pressure of the foot on the ground compresses the 

 india-rubber sole and diminishes the capacity of the included 

 air-chamber. A part of the contained air escapes by the con- 

 necting tube, and passes into the registering drum. 



We see in fig. 20 that the pressure of the right foot, for 

 instance, commences at the moment when that of the left 

 begins to decrease ; and that in all the tracings there is an 

 alternation between the impacts of the two feet. The period 

 of support of each foot is shown by a horizontal line which 

 joins the minima of two successive curves. 



The impacts of the right and left feet have the same dura- 

 tion, so that the weight of the body passes alternately from 

 one foot to the other. It would not be the same with respect 

 to a lame person ; lameness corresponds essentially with the 

 inequality of the impacts of the two feet. 



There is always a very short period during which the body 

 is partially supported by one foot, but when it already be- 

 gins to rest on the other ; this time is scarcely equal to the 



