THE ELASTICITY OF PASSIVE AND ACTIVE MUSCLE. 573 



just short of the point of rupture, varies for youth, middle and advanced age 

 approximately in the proportions 7 13 12. 



In the case of unorganized elastic bodies the amount of extension is always 

 directly proportional to the extending weight. In that of organized bodies, 

 therefore also of muscle, this is not the case, however, as with continued increase 

 in weight in equal amount they are extended less and less in the further course 

 of observation than at first. At the same time, they may for days or even weeks 

 gradually undergo a still further increase in length after the primary extension, 

 corresponding to the suspended weight, has been attained, if the same weight 

 be continued. This is designated elastic after-effect. 



The elasticity of passive muscle is small but complete, and is com- 

 parable to that of India rubber. The muscle can be greatly elongated 

 by means of small weights. With the uniform addition of further units 

 of weight, uniform extension, however, no longer takes place, but 

 a slighter increase in length corresponds with equal increments of 

 weight the greater the load. This phenomenon may also be expressed 

 as follows : the amount of elasticity of passive muscle increases with its 

 increased extension. 



Method. For the purpose of studying elasticity, the muscle is suspended 

 free from a support provided with a scale, and the lower extremity is loaded 

 successively with different weights placed in a small attached weighing-pan. The 

 resulting elongation is measured in each instance. To construct a curve of elonga- 

 tion, the units of weight added successively are taken as abscissas, and the lengths 

 corresponding to each load as ordinates. The following is an example from the 

 hyoglossus of the frog: 



Weight in 

 Grams. 



0-3 

 i-3 

 2-3 

 3-3 

 4-3 

 5-3 



The curve of elongation is not a straight line, as in the case of unorganized 

 bodies, but it resembles a hyperbola in form. The stretched muscle has a some- 

 what diminished volume, as have the contracted and the rigid muscle. 



Muscles permitted to retain their connections in the living animal with 

 their vessels and nerves are more extensible than excised muscles. Perfectly 

 fresh muscles elongate at first proportionately to the weight if the increase in 

 the latter be uniform and be kept within narrow limits, therefore like unor- 

 ganized bodies. If the weights be heavy the observations are not made without 

 consideration of the elastic after-effect. 



Dead, and especially rigid, muscle possesses a greater elasticity than fresh, 

 living muscle; that is a greater weight is required to stretch the former than is 

 needed to stretch the latter to the same length. On the other hand, the elas- 

 ticity of dead muscle is less complete; that is, after being stretched, it regains its 

 natural form only within narrow limits. 



In contradistinction from the elastic after-extension of muscle when weighted, 

 after the tension has become constant, Blix recognizes an after-contraction of 

 muscle, which comes into play after removal of the weight. Further, he dis- 

 tinguishes an after-relaxation in muscle that has been stretched, its tension in- 

 creasing with the increase in length, but diminishing when the length has become 

 constant; and, finally, an after-tension in a previously stretched muscle, whose 

 length is diminished, the previously low tension again increasing, when the length 

 has become constant. 



In the intact body the muscles are already stretched to a slight extent, as 

 indicated by the moderate retraction that usually takes place when the muscular 

 insertion is detached. This slight degree of extension is of importance with the 

 occurrence of contraction; as otherwise the muscle would first have to contract, 

 without immediately entering into activity, before it could exert traction upon 

 the bones. The elasticity of the muscles becomes evident on the contractions of 



