492 



ELASTIC AFTER-EFFECT. 



Elastic After-Effect. At the same time, after the first elongation, correspond- 

 ing to the extending weight, is reached, the muscle may remain for days, and even 

 weeks, somewhat elongated. This is called the "elastic after-effect" ( 65). 

 [Marey attached a lever to a frog's muscle, and allowed the latter to record its 

 movements on a slowly revolving cylinder. To the lever was fixed a vessel into 

 which mercury slowly flowed. This extended the muscle, and when it had ceased 

 to elongate, the mercury was allowed slowly to run out again. The curve obtained 

 is shown in fig. 342. The absciss*, o x and x, indicate the position of the writing- 

 style before and after the experiment, and we observe that x is lower than o x, so 

 that the recoil is imperfect. There has been an actual elongation of the muscle, 

 so that the limit of its elasticity is exceeded. Although a frog's gastrocnemius 

 may be loaded with 1500 grammes without rupturing it, 100 grammes will prevent 

 its regaining its original length.] 



Method. In order to test the elasticity of a muscle, fix it to a support provided with a 

 graduated scale, and to the lower end of the muscle attach a scale-pan, in which are placed 

 various weights, measuring on each occasion the corresponding elongation of the muscle thereby 

 obtained {Ed. Weber). In order to obtain the curve of elongation or extensibility take as 

 abscissa? the successive units of weight added, and the elongation corresponding to each weight 

 as ordinates. Example from the hyoglossus of the frog : 



The elasticity of passive muscle is small, but very complete, and is comparable 

 to that of a caoutchouc fibre. Small weights greatly elongate the muscle. If the 

 weights be uniformly increased, there is not a uniform elongation ; with equal 

 increments of weight, the greater the load, the increase in elongation always 

 becomes less; or, to express it in another way, the amount of elasticity of the 

 passive muscle increases with its increased extension (Ed. Weber). 



In inorganic bodies, the curve of extension is a straight line, but in organic 

 bodies, it more closely resembles a hyperbola (Wertheim). The elasticity of a 

 passive fatigued muscle does not differ essentially from that of a non-fatigued 

 muscle. 



Muscles in the living body, and still in connection with their nerves and blood-vessels, are 

 more extensible than excised ones. Muscles, when quite fresh, are elongated (within certain 

 small limits as regards the weight) at first with a uniformly increasing weight, to an extent 

 proportional to the latter, just as with an inorganic body. When heavy weights are used, we 

 must be careful to take into consideration the "elastic after-effect" ( 65). 



The volume of a stretched muscle is slightly less than an unstretched one, similar to the 

 contracted ( 297, 2) and stiffened muscle ( 295). 



Dead muscles and muscles in rigor mortis have greater elasticity, i.e., they require a heavier 

 weight to stretch them than fresh muscles ; but, on the other hand, the 'elasticity of dead 

 muscles is less complete, i.e., after they are stretched, they only recover their original form 

 within certain limits. 



Elasticity of Intact Muscles. Normally, within the body, the muscles are 

 stretched to a very slight extent, as can be shown by the slight degree of retraction 

 which occurs when the insertion of a muscle is divided. This slight degree of 

 extension, or stretching, is important. If this were not so, when a muscle is about 

 to contract, and before it could act upon a bone as a lever, it would have to " take 

 in so much slack." The elasticity of muscles is manifested during the contraction 



