400 MUSCULAR MOTION. 



During contraction, the muscle is sometimes so rigid and elastic as 

 to be capable of vibration when struck. The ordinary firm state is well 

 exhibited by the masseter, when the jaws are forcibly closed ; and some 

 men possess the power of producing sonorous vibrations by striking the 

 contracted biceps with a metallic rod. 



It has been a matter of dispute whether the quantity of blood circu- 

 lating in a muscle is diminished during contraction. At one time, it 

 was universally believed, that such diminution existed, and that it ac- 

 counted for the diminished size of the muscle during contraction. This 

 last allegation we have shown to be inaccurate; and no correct deduc- 

 tion can, consequently, be drawn from it. Sir Anthony Carlisle 1 

 adopted the opinion, that the muscles become pale during contraction; 

 but he offers no proof of it. The probability is, that he implicitly 

 obeyed, in this respect, the dicta of his precursors, without observing 

 the incongruity of such a supposition with his idea, that the absolute 

 size of the muscle is augmented during contraction. The truth is, we 

 have no evidence, that the colour of a muscle, or the quantity of blood 

 circulating in it, is altered during contraction. Bichat, 2 who adopted 

 the opinion, that the blood is forced out during this state, relies chiefly 

 upon the fact, known to every one, that in the operation of blood-letting 

 from the arm the flow of blood is augmented by working the muscles; 

 but the additional quantity expelled is properly ascribed by Dr. Bos- 

 tock 3 to the compression of the large venous trunks by the swelling 

 out of the bellies of the muscles. The prevalent belief, amongst phy- 

 siologists of the present day, is, that there is no change of colour in 

 the muscle during contraction. 



When the extremities of a muscle are made to approximate, the 

 belly, of course, swells out; and would probably expand to such an 

 extent, that the fasciculi, of which it is composed, would separate from 

 each other, were it not for the areolar membrane and aponeuroses, 

 with which they and the whole muscle are enveloped. 



The phenomena attendant upon the relaxation of a muscle are the 

 reverse of those that accompany its contraction. The belly loses its 

 rugous character; becomes soft, and the swelling subsides; the ends 

 recede, and the organ is as it was prior to contraction. It is obvious, 

 however, that after a part, as the arm, has been bent by the contrac- 

 tion of appropriate muscles, simple relaxation would not be sufficient 

 to restore it to its original position; for although the relaxation of a 

 muscle has been regarded by Bichat and others to be, in part at least, 

 an active effort; and to consist in something more than the mere ces- 

 sation of contraction, the evidence in favour of the view is extremely 

 feeble and unsatisfactory. The arrangement of the muscular system 

 is, in this, as in every other respect, admirable, and affords signal evi- 

 dence of Omnipotent agency. The arm, as in the case selected above, 

 has not only muscles to bend, but also to extend it; and, accordingly, 

 when it has been bent, and it becomes necessary to extend it, the flexor 

 muscles are relaxed and rest, while the extensors are thrown into 



1 Op. citat, p. 27. a Anat. General., torn. iii. 2. 



3 Physiology, 3d edit., 94, Lond., 1 836. 



