192 



HUMAN PHYSIOLOGY 



Extensibility of the tetanized muscle. The tetanized 

 muscle is more extensible than the resting muscle. The 

 curve of its extensibility resembles a hyperbola, but its 

 course is steeper than that of a resting muscle (Fig. 10). 



w 



20 



30 



\ 

 a \ 



40 



D 



B 



FIG. 10. CURVES OF EXTENSIBILITY OF A RESTING AND AN ACTIVE MUSCLE 



(DIAGRAMMATIC). 



a, b, c, d, e, are the length of a resting muscle loaded with o, 10, 20, 30, 40 

 grams; the curve AB which joins the ends of these perpendiculars represents the 

 curve of extensibility. Correspondingly, CD represents the curve of extensibility 

 of the tetanized muscle. 



Continuous contraction not tetanic. By the action of con- 

 tinuous stimuli upon muscles (e.g. stimulation by ammonia, 

 a constant current) a continuous contraction is produced, of 

 which it has not been proven that it is produced by the 

 combination of twitches. 



(b} Work done by a stimulated muscle. The work done 

 is the product of the weight raised by the height to which it 

 is raised. Other things being equal, the height of the con- 

 traction is proportional to the length of the fibres. 



The force with which the weight is raised is, other things 

 being equal, proportional to the cross-section of the muscle. 

 In muscles in which the fibres run obliquely, the so-called 

 physiological cross-section, that is, the cross-section of all 

 the fibres, must be taken into consideration. 



The absolute force of the muscle is equivalent to the 

 weight which just prevents the contraction of a maximal 

 tetanized muscle. The absolute force of the striated frog- 



