574 



THE ELASTICITY OF PASSIVE AND ACTIVE MUSCLE. 



its antagonists. The position of a passive limb depends upon the resultant of 

 the elastic traction of the various muscle-groups. 



The elasticity of active muscle is diminished as compared with that of 

 passive muscle; that is it is lengthened by the same weight to a greater 

 extent than is resting muscle. For this reason active muscle is softer, 

 as can be demonstrated in an excised, contracted muscle. The appar- 

 ently increased hardness of tense, contracted muscles is due only to their 

 tension. When an active muscle becomes fatigued, its elasticity is still 

 further diminished. During the latent period, in which the develop- 

 ment of electrical phenomena and of heat points to metabolic activity in 

 the muscle, no change in elasticity has as yet been demonstrated. 



Method. Ed. Weber made observations in the following manner. The hyo- 

 glossus muscle of the frog was suspended vertically, and its length was measured 

 in the passive state. The muscle was then tetanized by induction-shocks and 

 again measured. Progressively increasing weights were then attached to it, in 

 succession, and the amount of stretching of the passive and then the length 



FIG. 198. Blix's Elasticity Recorder. 



of the tetanized muscle (supporting the same weight) ascertained. The extent 

 to which the active, weighted muscle contracted from the passive, weighted 

 condition is termed the height of the lift. This becomes steadily less as the weight 

 increases, until finally the heavily weighted, tetanized muscle can no longer con- 

 tract; that is the height of the lift is zero. Indeed, if the weight be exceedingly 

 heavy it may happen that the muscle, when stimulated, not only can contract 

 no further, but it may even elongate. According to Wundt, however, the elas- 

 ticity of the muscle does not change under such conditions. In these observations 

 the length of the active, weighted muscle is equal to the length of the equally 

 weighted, passive muscle, minus the height of the lift. 



Tracings of the length-curves recorded by passive or contracting muscle 

 stretched by weights can be conveniently made by means of the apparatus of 

 Blix, as shown in Fig. 198. The rectangular piece (A B C) is movable hori- 

 zontally between two strips (R R). To the vertical portion of the former is 

 attached the freely suspended muscle (m), which is connected with the writing- 

 lever (S S), the latter being attached to the horizontal portion near C by means 

 of a hinge- joint. The writing-lever is provided with a small movable rod (dd), 

 from which a weight is suspended. When the rectangular piece (A B C) is 

 moved in the direction of the arrow, the weighted rod (d d) more closely ap- 

 proaches the muscle, which thus becomes constantly more and more heavily 

 weighted. 



With the muscle at rest (m) the curve o a b c e is first recorded by means 

 of the displacement described. Then a similar curve is recorded while the muscle 



