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The mechanism of running is a compound of that of walking and 

 leaping, but resembling most the latter 5 hence some authors have defin- 

 ed it to consist of a succession of low leaps. The steps are not longer 

 than in walking, but merely succeed each other with greater velocity. 

 The centre of gravity is transferred, with more rapidity, from one leg to 

 the other, and falls are much more apt to take place. The quick repeti- 

 tion of the same motions, in running, requires a very lively contractility 

 in the muscles which move the extremities, and as the energy of this vital 

 property is proportioned to the extent of respiration, to the quantity of air 

 which the blood acquires in passing through the lungs; in running, we 

 pant and breathe frequently, and at short intervals, without any particu- 

 lar enlargement of the chest, at each act of respiration. It was necessary 

 that the parietes of this cavity should, in running, be remarkably fixed ; 

 for, it becomes the point on which those muscles are inserted which 

 steady the pelvis and loins, and prevent their yielding an unsteady basis 

 to the lower extremities. The best runners are those who have the 

 strongest lungs, that is, who can give to the chest the greatest degree of 

 permanent dilatation. In contending for the prize in running, you may 

 see them throw back their head and shoulders, not only to obviate the 

 propensity which there is in the line of the centre of gravity to fall to- 

 wards the anterior plane, but likewise, that the cervical column, the sca- 

 pulae, the clavicks, and the humerus, being fixed, may furnish a firm at- 

 tachment to the auxiliary muscles of respiration. 



We should run with much less speed, if we applied to the ground the 

 whole soal of the foot; partly from the time which would be taken up in 

 thus applying the foot to the ground, and partly by the friction which 

 would necessarily take place. Hence, in running, we generally touch the 

 ground with the end of the foot. We run with most speed, when the 

 foot is in a state of extension, the leg being moved rapidly by the exten- 

 sors of the knee. This accounts for the tendency which there is to fall 

 while we run, the centre of gravity obeying the impulses which follow 

 each other in rapid succession, and never resting but on a basis of very 

 limited extent. Another reason why the slightest unevenness of the 

 ground is apt to occasion falls in running, is, that the rapid motion com- 

 municated to the body by the sudden and perpetually recurring exten- 

 sions of the posterior extremity, increases at every step, so that it is im- 

 possible to stop suddenly, and without having previously slackened one's 

 pace, and moderated the impulse to which the body is subjected. 



As it is mostly forward that falls are apt to take place, in running we 

 always throw back the head, and make use of our arms to balance the 

 body, so that they may be in constant opposition to the legs, that is, that 

 the right lower extremity, for example, being carried forward, the left arm 

 may be balanced backward, 



Few animals are better formed than man to run with speed, his lower 

 limbs are in ienght equal to one half of the whole length of the body, and 

 the muscles which move them are very powerful ; hence, savages, who 

 are in the constant habit of running, overtake the animals which they 

 make their prey ; and, even in Europe, there are professed runners who 

 equal in swiftness the fleetest horses. This animal, like every other swift 

 quadruped, would move much more slowly than man, on account of the 

 number of the limbs on which he rests, if he had not the power of mov- 

 ing them in pairs, and thus reducing his legs to two, as in what is called 

 full gallop. 



