PRACTICAL PHYSIOLOGY 43 



length to which the resting 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 curve of extension of the contract- 

 ing 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. 



3. The effect of after-loading. Take a series of 

 contraction ordinates, using a maximal stimulus 

 and a constant weight (say about thirty grammes). 

 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 some- 

 what slackened. Under these circumstances the 

 muscle will not begin to raise the weight until its 

 contraction has proceeded to a certain extent ; this 

 is termed after-loading. Describe a series of con- 

 traction ordinates with a gradual increase of after- 

 load. Estimate the amount of work done under 

 these conditions, and compare with that performed 

 by the free-weighted muscle. 



These experiments on muscle work and exten- 

 sion can be performed either with single make or 

 break shocks, or by. tetanisation by means of the 

 Neef s hammer of the induction coil. 



