130 



ANIMAL MECHANISM. 



reach its minimum, at the moment when one foot has just 

 risen, and before the other has reached the ground. 



This relation of the vertical oscillations to the pressure 

 of the feet shows plainly that the time of suspension does not 

 depend on the fact that the body, projected into the air, has 

 left the ground, but that the legs have withdrawn from the 

 ground by the effect of their flexion ; and this takes place at 

 the very moment when the body was at its greatest elevation. 



We shall have again to recur to these phenomena when we 

 come to speak of the paces of the horse, in which a similar 

 suspension of the body exists, and which are called on that 

 account elevated paces. 



The influence of the different inclinations of the ground 

 acts in nearly the same manner in running as in walking, 

 with this difference, that in running, their effects are generally 

 greater. 



3. Of the gallop. — In the modes of progression described 

 hitherto, the movement of the limbs is regularly alternate, so 

 that the succession of steps is made at equal intervals. 

 These are the normal kinds of human locomotion ; but man 

 can imitate, to a certain extent, by the movements of his feet, 

 those periodically irregular cadences which are produced by a 

 horse when he gallops. Children, in their amusements, often 

 imitate this mode of locomotion, when they play at horses. 

 This abnormal kind of motion is of no interest, except to 

 explain the mechanism of the gallop in quadrupeds. 



By registering together the step-curves and the re-actions, 

 it is seen (fig. 31) that the foot placed behind is the first 

 which reaches the ground; that it exerts an energetic and 

 prolonged pressure, towards the end of which the foot in front 

 touches the ground in its turn, but during a shorter time ; 

 after which there is a considerable period of suspension. 

 Thus, there is a moment when the two feet are in the air. 



In this mode of progression, the re-actions are similar in 

 character, in some respects, to the pressures. In fact, a long 

 re-action (line O) is produced, in which we recognise the 

 interference of two vertical oscillations, the second of which 

 commences before the first has finished. After this re-action 

 there is observed a lowering of the curve, whose minimum 



