224 



PHYSIOLOGY 



over-shoot of the lever whenever, as at high temperatures, the con- 

 traction is sufficiently rapid. The effect of this is that one cannot 

 assume the existence of an actual pull on the lever during the whole 



FIG. 58. V. Kries' apparatus for taking ' after -loading ' and ' arrested 



contraction ' curves. 



time of the ascent of the latter. We can therefore speak of a period 

 during which there is contractile stress that is to say, when the muscle 

 is actually pulling on the lever, which will occupy only a part of the 



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FIG. 59.^ Curves of isotonic and arrested contractions of an 

 unloaded muscle. (KAISEE.) 



ascent of the curve. The duration of this period of contractile stress 

 may be shown'byjecording what is known as ' arrested ' contractions. 

 One mechanism for this purpose is shown in the figure (Fig. 58). The 

 stop Su is used simply for after-loading the muscle so that the weight 

 shall not act upon the muscle until it begins to contract. The stop 

 So may be regulated so that it suddenly checks the movement of the 

 lever at any desired height above the base line. We may thus get a 



