3 68 



THE PROPERTIES OF STRIPED MUSCLE. 



the interval of time between the moment of encounter and that of culmination 

 diminishes In this case each response begins isotonically, and proceeds 

 isometricaUy, as seen in Fig. 198.1 When the lever, on the relaxation of the 

 muscle, leaves the stop, the curve again follows an isotonic course. 



To make clear the bearing of these empirical data, some further explanation 



is neee^ary The reader must first understand that the purpose of both the 



methods above described is to investigate at any moment in the response, the 



two functional activities (Leistungsfahigkeiten) of a muscle— the Fahigkeit 



Verteirzung zu leisten, and the Fahigkeit Spawning zu erzeugen. These are 



represented by the slant of the isometric and isotonic curves respectively, at 



the moment that the lever parts from So or encounters Su. To indicate these 



times the vertical broken lines have been added to von Kries' figure. The 



important point in the curve of after -loading is that whereas the isotonic 



curve rises with an initial inclination which diminishes as the load increases, 



the isometric has nearly the same initial inclination throughout. This means 



that " the ability of the muscle to generate tension " is unchanged, while its 



"ability to produce shortening" diminishes. The relation between these he 



calls " the apparent extensibility " of the muscle. In the experiment given in 



Big. 198, the load which is at first minimal is increased after each observation ; 



but as it is not 

 supported, the lift 

 begins at a lower 

 and lower level. 

 At the moment of 

 arrest, which of 

 course occurs later 

 and later, the length 

 of the muscle is 

 always the same. 

 Its rate of shorten- 

 ing diminishes as 

 in the previous 

 case, but its rate of 

 increase of tension 

 is not constant as 

 before, but dimin- 

 ishes with the rate 

 of shortening ; so 

 tha< the " apparent extensibility " remains nearly the same. The explanation 

 n by v. Kries is as follows:— In a muscle, notwithstanding that length 

 tension remain the same, the relation between the two functional 

 capacities differs according to the "way in which the portion of the 

 respon e which precedes the transition" has occurred (see p. 369). He 

 sapposee that what happens at the beginning of the contraction influences 

 the subsequent Btate of the muscle by its influence in determining the 

 of fibres which participate in the process, and surmises that the 

 initial tension (starke Spannung im Moment der Reizung) is to 

 i number of acting fibres, and thereby to bring about a con- 

 v.hirh the rate of change of tension corresponds to that of change 

 Lhe data seem to me to admit of a simpler explanation. The 

 lie stores* of the muscular fibres at the moment of transition is in each 

 ily indicated by the rate of augmentation of tension— that is, by the 

 '■"Hal inclination oi the isometric curve, and is accordingly greater in the first 

 than at the corresponding period in the second. But the reason why 

 thai tl„. measurements relating to the first series are made at an 



' v - lu " •'■<■/'./. Physiol., Leipzig, 1892, S. 10. 



FlG. 198. -Series of " arrested contraction " curves, with increasing 

 load, tli'- Length of the muscle being the same at the moment 

 ofarresl is each case. — After v. Kries. 



effeel of 

 augmenl 

 dition iu 



<>! form. 





