292 OF MUSCULAR CONTRACTILITY. 



opposite scale, he allowed the muscle to relax until it was extended to a certain 

 point, and then ascertained the weight which would balance its power. The 

 same was several times repeated, as in the following manner. The length of 

 the muscle in its extreme state of contraction, at which no additional force 

 could be exerted by it, being represented by 14, it was found that, when it 

 had been extended to 17, it would balance a weight of 60 ; when its length 

 increased to 19-6, it would balance a weight of 120 ; and at 22-5, it would 

 balance 180. In another experiment, the muscle at 13-5, balanced 0; at 

 18-8, it balanced 100; and at 23-4, it balanced 200. Hence it appears that 

 an uniform increase of force corresponds with a nearly uniform increase in the 

 length of the muscle ; or, in other words, that when the muscle is nearly at 

 its full length, its contractile power is the greatest. In later experiments upon 

 the same muscle, this uniform ratio seemed to be departed from ; but by com- 

 paring the results in a considerable number of instances, it was constantly 

 found that in those experiments which were performed the soonest after the 

 preparation of the frog, and in which, therefore, the normal conditions of the 

 system were the least disturbed, the ratio was very closely maintained. It 

 has been hence inferred by Miiller, that the power which causes the contrac- 

 tion of a Muscle must be very different in its character, from any of the forces 

 of attraction known to us ; since these all increase in energy as the attracted 

 parts approach each other, in the inverse ratio of the square of the distance ; 

 so that the power of a Muscle, if operated on by any of these, ought to increase, 

 instead of regularly diminishing, with its degree of contraction. But it is to 

 be remembered that, as the observations of Mr. Bowman have clearly shown, 

 there must be a considerable displacement of the constituents of every fibre 

 during contraction (371) ; so that it is easy to understand that the greater the 

 contraction, the more difficult must any further contraction become. If, be- 

 tween a magnet and a piece of iron attracted by it, there were interposed a 

 spongy elastic tissue, the iron would cease to approach the magnet at a point, 

 at which the attraction of the magnet would be balanced by the force needed 

 to compress still further the intermediate substance. 



VI. Applications of Muscular Power. 



395. The energy of Muscular contraction is of course to be most remark- 

 ably observed in those instances in which the continual exercise of particular 

 parts has occasioned an increased determination of blood towards them, and 

 in consequence a permanent augmentation in their bulk. This has been the 

 case, for example, with persons who have gained their livelihood by exhibit- 

 ing feats of strength. Much will, of course, depend on the mechanically 

 advantageous application of muscular power ; and in this manner effects may 

 be produced, even by persons of ordinary strength, which would not have been 

 thought credible. In lifting a heavy weight in each hand, for example, a 

 person who keeps his back perfectly rigid, so as to throw the pressure verti- 

 cally upon the pelvis, and only uses the powerful extensors of the thigh and 

 calf, by straightening the knees (previously somewhat flexed), and bringing 

 the leg to a right angle with the foot, will have a great advantage over one 

 who uses his lumbar muscles for the purpose. A still greater advantage will 

 be gained, by throwing the weight more directly upon the loins, by means of 

 a sort of girdle, shaped so as to rest upon the top of the sacrum and the ridges 

 of the ilia ; and by pressing with the hands upon a frame, so arranged as to- 

 bring the muscles of the arms to the assistance of those of the legs ; in this 

 manner, a single man of ordinary strength may raise a weight of 2000 Ibs. ; 

 whilst few who are unaccustomed to such exertions, can lift more than 300 

 Ibs. in the ordinary mode. A man of great natural strength, however, has 

 been known to lift 800 Ibs. with his hands : and the same individual 



