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 strize 
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 muscular 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 fibrille) 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 muscular 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 of 
muscular fibre, ¢ritability 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 
