40 



EXPERIMENTAL PHYSIOLOGY 



muscle is extended by the particular weight, and the top of the ordinate the 

 length to which the muscle when contracted is extended by the same weight. 

 If the ordinates are at regular distances apart, a line joining their lowermost 

 ends gives the curve of extension of the resting muscle, and a line joining the 

 tops of the ordinates the curves of extension of the contracting muscle. Further, 

 if the weights are removed in succession and ordinates are again described after 

 each such removal, curves of recovery from extension i.e. of retraction can 

 be obtained. This experiment can be conveniently performed with the sartorius, 

 large shot serving as the weights. 



I 



FIQ. 38. EXPERIMENT FOR INVESTIGATING THE EFFECT OF HEAT ON THE EXTENSIBILITY 



OF MUSCLE. 



3. The effect of after-loading (p. 27). Take a series of contraction 

 ordinates, using a maximal stimulus and a constant weight (say 

 about thirty grams). Begin with the muscle free- weighted, and by 

 using the screw stop beneath the lever raise the latter so that the 

 muscle and connecting thread are somewhat slackened. Under these 

 circumstances the muscle will not begin to raise the weight until its 

 contraction has proceeded to a certain extent ; this shows the effect 



