128 



ANIMAL MECHANISM. 



Nothing like this is observed in the descent of a staircase ; 

 the step-curves cease to encroach on each other, and succeed 

 each other very nearly as in ordinary walking on level 

 ground. 



Fig. 29. — Tracing produced by walking upstairs. D. tracing of the pressure 

 and rise of the right foot (full line). G. tracing of the left foot (dotted 

 line). It is seen that the curves produced by the feet encroach one on the 

 other, and that the maxima of the pressures of the feet correspond with 

 the end of the pressures. 



2. Of running. — This mode of progression, more rapid 

 than walking, consists, like it, in alternate treads of the two 

 feet, whose step-curves follow each other at equal intervals ; 

 but it presents this difference, that in running, the body 

 leaves the ground for an instant at each step. 



Accordingly, as running is more or less rapid, different 

 names are given to it ; those of the gymnastic march and the 

 trot present no utility in a physiological point of view ; they 

 correspond, with but slight variations, to running at various 

 degrees of speed. To ascertain the principal characters of 

 this mode of progression, it is only necessary to analyse 

 fio-. 30. 



Fig. 30. — Tracing produced by running (in man). D. (curve formed by a 

 full line), impact and rise of right foot. G. (dotted line) action of the left 

 foot. O. oscillations and vertical re actions of the body. 



The pressures of the feet are more energetic than in 

 walking; in fact, they not only sustain the weight of the 



