200 



PHYSIOLOGY 



on to consider the changes which occur in the muscle between the application 

 of the stimulus and the moment at which the first mechanical change makes 

 its appearance. 



The relaxation of muscle is helped by a moderate load, and in a normal 

 condition is complete. It is not active that'is to say, is not due to a con- 



FIG. 59. V. Kries 1 apparatus for taking ' after- loading ' and 'arrested con- 

 traction curves.' 



traction in the transverse direction but is a passive effect of extension and 

 elastic rebound. This may be shown by allowing a muscle to contract while 

 floating on mercury. The subsequent lengthening on relaxation is very 

 incomplete. 



Even with the most careful arrangements for securing isotonicity in the 

 record of the contraction there is probably a certain amount of over-shoot 

 of the lever whenever, as at high temperatures, the contraction is sufficiently 

 rapid. The effect of this is that one cannot assume the existence of an act ual 

 pull on the lever during the 

 whole 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 actu- 

 ally pulling on the lever, which l 

 will occupy only a part of the AAAAAAAAAAAAAAAAAAAAA 

 ascent of the curve. The dura- _ 



. , , . . , , FIG. 60. Curves of isotonio and arrested contractions 



lion Ot this period Ot COntraC- O f an unloaded ...nsclr (KAISER.) 



tile stress may be shown by 



recording what is known as anvMt-d ' c -ontrac-.tions. One mechanism 



for this purpose is shown in the figure (Fig. 59). The stop Su is 



