146 Miscellaneous. 



mechanical extension followed by retraction, or whether they are 

 produced apparently spontaneously, observation proves that in either 

 case the alternate changes which the contractile organ undergoes 

 are identical. In a muscular fibre which, after mechanical extension, 

 returns upon itself in virtue of its elasticity, the transverse striae 

 change their aspect and approach each other, at the same time that 

 the transverse diameter increases in proportion to the diminution of 

 the length. It is exactly in the same way that the muscular fibre 

 behaves in passing from the state of elongation corresponding with 

 the repose of the muscle to the state of active shortening designated 

 by the name of muscidar contraction. If the essential phenomena 

 by which muscular contraction is manifested are identical with those 

 of the elastic contraction of muscles — if, on the other hand, the 

 elementary structure of contractile organs appears specially adapted 

 to the manifestations of elasticity, we may justly ask whether it is 

 necessary to invoke, in order to explain the shortening of muscle in 

 the state of contraction, a special property of contractility, distinct 

 from the properties of inorganic matter. 



Elasticity may become a cause of movement in two opposite condi- 

 tions : — 



Either the elastic body, the spiral spring, is subjected to a pres- 

 sure which keeps the turns of the spiral in a forced approximation, 

 when, on the pressure ceasing, the turns separate, the spring elon- 

 gates and moves by the mere fact of its elasticity ; or the spring is 

 subjected to a tension which elongates it by separating the turns of 

 the spiral from each other ; on the tension ceasing, the turns ap- 

 proach each other, and the spring moves by shortening, without 

 anything but elasticity coming into play. 



The alternations of elongation and shortening of the elastic ele- 

 ments {spiral f brill (b) of the muscles might therefore be explained 

 by elasticity alone, if we demonstrated the existence either of an 

 agent of pressure exercising its action during the period of shorten- 

 ing, or of an agent of extension acting during the period of elonga- 

 tion^ — the muscle elongating in the former case and shortening in 

 the latter by the free play of elasticity the moment the action of an 

 antagonistic force ceases to equilibrate it. 



The physiological problem of nruscular movement is thus brought 

 to its most simple terms — to determine the natural form (the state 

 of repose) of the muscular spring, the conditions which can remove 

 it therefrom, and those to which elasticity recalls it. 



There are at present two hypotheses as to the cause of muscular 

 movement : one attributes this movement to a special property uf 

 muscular fibre, irritahility or contractility, which manifests itself 

 only in the period of activity of the muscle and produces the short- 

 ening ; the other, on the contrary, regards the shortening as the 

 return of the muscle to a state of repose. This latter hypothesis, 

 which supposes that, during the period of apparent inactivity of the 

 muscle, the nerves are constantly at work to maintain the forced 

 extension of the contractile fibres, is certainly refuted by the incon- 

 testible fact that the section of the motor nerves does not cause the 



