288 PEACTICAL PHYSIOLOGY 



nil. Hence a muscle would contract under the most favourable 

 circumstances, if the load, as it was raised, progressively decreased. 

 Relation of Load to Work done during Contraction. In order to 

 record the height of contraction for a large range of weights, it is 

 more convenient to record on a stationary drum simply the heights 

 of a series of twitches than to super-impose a large number of curves. 

 The apparatus is arranged for stimulating the muscle with a single 

 maximal induction-shock, using a simple key in the primary circuit. 

 A weight is hung near the axis of the lever of such a size that the 

 actual load on the muscle is 50 grms. ; the method of calculating 

 this weight has been already given on p. 29. The muscle is just 

 completely after-loaded throughout the experiment in order to get 

 rid of the effect of alterations in the initial tension. With the lever 

 horizontal, the muscle is stimulated, and the height of its contrac- 

 tion recorded on a stationary drum. The drum is rotated a short 

 distance by hand ; an additional load of 50 grms. is hung from the 

 lever, and another contraction recorded. The process is repeated 

 until the muscle is no longer able to raise the load off the after- 

 loading screw. Fig. 172 gives the result of such an experiment; in 

 it the magnification was 5, and the actual load on the muscle half 

 of the weight hung near the axis of the lever. The following table 

 gives in grm. mm. the work done by the muscle with the various 

 loads. 



Actual load in grm. Actual lift in mm. Work in grm. mm. 



50 4-0 200 



100 3-2 320 



150 2"2 330 



200 -1-8 360 



250 1-2 300 



300 1-0 300 



350 -8 280 



400 -5 200 



450 '4 180 



500 -3 150 



550 -2 110 



600 -1 60 



700 



From the last column in this table we see that, although the height 

 of the contractions diminishes continuously, the actual work done by 

 the muscle increases at first rapidly and then more slowly, until it 

 reaches its maximum with a load of 200 grms. After that point 

 the work done begins to decrease slowly, and then more rapidly 

 until at 700 grms. a load is reached which the muscle is unable to 



