526 



MUSCULAR MOTION. 



the mode and duration of action of the force 

 itself. Thus sifted, they prove that, even when 

 directly stimulated by water after removal from 

 the body, a muscle contracts in successive por- 

 tions, never in its totality at once, and that no 

 particle of it is capable of exhibiting an active 

 contraction for more than an instant of time. 



The appearances presented by muscle that 

 has been ruptured by its own inordinate con- 

 traction in fatal tetanus in the human subject 

 will supply the link wanting to connect the 

 foregoing phenomena with those occurring in 

 healthy contraction during life : for tetanic 

 spasm differs from sustained voluntary contrac- 

 tion only in its amount and protracted duration, 

 and in its being independent of the will ; none 

 of which circumstances are of essential import- 

 ance in regard to the nature of the act of con- 

 traction itself. 



The muscles are so arranged in the body 

 that no amount of contraction which the me- 

 chanism of the bony and ligamentous frame- 

 work will permit one of them to undergo, can 

 by possibility occasion the ruptuie of a relaxed 

 antagonist: to be ruptured the antagonist must 

 be itself contracted. But a muscle, if contract- 

 ing beyond its natural amount, may be so re- 

 sisted by mechanical powers, in or out of the 

 body, as to rupture itself. Hence, the contrac- 

 tion of a muscle is a necessary condition, and 

 generally the essential cause of its own rupture : 

 the other condition being a force greater than 

 the tenacity of the ruptured part, holding its 

 ends asunder ; this latter may be either the 

 active or passive contraction of antagonists, or 

 mere mechanical resistance. But it is evident 

 that for a muscle to be ruptured by its own 

 contraction, that contraction must be partial, as 

 is shewn in the case of the Frog's muscle 

 already mentioned. An examination of muscle 

 ruptured in tetanus is found to bear out these 

 observations in the fullest manner.* The ele- 

 mentary fibres present numerous bulges of a 

 fusiform shape, in which the transverse stripes 

 are very close. These swellings or contracted 

 parts are separated from one another by inter- 

 vals of various lengths, in which the fibre has 

 either entirely given way or is more or less 

 stretched and disorganized. These appearances 

 are met with after all contractility has departed ; 

 they are the vestiges of the spasm during life. 

 Yet in other muscles, which have been likewise 

 convulsed, but not ruptured, they are not 

 found. Their presence is, therefore, the result 

 of the rupture. They admit only of the follow- 

 ing explanation : the contractile force has ope- 

 rated at the points contracted, and by its excess 

 the intermediate portions have been stretched to 

 laceration. Having once given way, the con- 

 tracted parts have become isolated, and can no 

 longer have been extended after the subsidence of 

 their contractile force ; they consequently retain 

 the form and appearances they possessed, when 

 surprised, as it were, by the rupture they have 

 themselves produced of the intervening parts. 



Supposing, for a moment, that active con- 

 traction were a universal and equable act, and 



* Phil. Trans. 1841, p. 69. 



that by the superior power of an antagonist a 

 weak muscle had been ruptured, the appear- 

 ances resulting would manifestly be entirely 

 different from those now detailed. The fibres 

 beyond their ruptured point would have their 

 transverse stripes uniformly approximated. 



From the preceding facts I conclude, 1st, 

 that active contraction never occurs in the whole 

 mass of a muscle at once, nor in the whole of 

 any one elementary fibre, but is always partial 

 at any one instant of time; 2dly, that no active 

 contraction of a muscle, however apparently 

 prolonged, is more than instantaneous in any 

 one of its parts or particles ; and therefore, 

 3dly, that the sustained active contraction of a 

 muscle is an act compounded of an infinite 

 number of partial and momentary contractions, 

 incessantly changing their place, and engaging- 

 new parts in succession ; for every portion of 

 the tissue must take its due share in the act. 



Two phenomena yet remain to be mentioned, 

 which, by admitting of a satisfactory explana- 

 tion on this view of the subject, give strong 

 testimony to its correctness. The first is the 

 muscular sound heard on applying the ear to a 

 muscle in action. It resembles, according to 

 Dr. Wollaston's apt simile,* the distant rumb- 

 ling of carriage wheels, or an exceedingly rapid 

 and faint tremulous vibration, which, when well 

 marked, has a metallic tone. It is the sound of 

 friction, and appears to be occasioned by those 

 movements of the neighbouring fibres upon one 

 another, with which the partial contractions 

 must be attended in their incessant oscillations. 

 The other phenomenon is one, the existence of 

 which has been recently ascertained by MM. 

 Becquerel and Bieschet,f viz. that a muscle 

 during contraction augments in temperature. 

 They have found this increase to be usually 

 more than 1 Fahr., but sometimes, when the 

 exertion has been continued for five minutes, 

 as in sawing a piece of wood, it has been double 

 that amount. This development of heat seems 

 to be in a great measure attributable to, and 

 even a necessary consequence of, the friction 

 just alluded to. 



Thus it would appear that active contraction 

 consists in a disturbance of that state of equili- 

 brium ordinarily existing in muscles when at 

 rest; that their different portions successively 

 undergo momentary contractions, and that there 

 is always a considerable part of each fibre un- 

 contracted. This will account for the remark- 

 able fact that detached fragments of the volun- 

 tary fibre will contract by two-thirds of their 

 length, though an entire muscle, in its natural 

 situation, cannot shorten by more than one- 

 third. This great capacity of contraction in the 

 tissue would be without a purpose, if it were 

 not that it only admits of momentary exertion, 

 and therefore requires that in the organ succes- 

 sive parts should take up the act, and by so 

 doing, render it, as a whole, continuous. In an 

 active fibre the contracting parts are continually 



* Phil. Trans. 1811. 



f Recherches sur la chaleur animale, an moyen 

 des appaveils thermo-electriques ; par MM. Bee 

 querel et Brescliet, Membres de 1'Inslitut. Archives 

 du Museum, torn. i. p. 402. 



