MUSCLE 



243 



muscle, since eacli muscle can contract to a fixed proportion 

 of its original length. A glance at the diagram will at once 

 make this plain (fig. 124). The size of the muscle is thus 

 the first great factor which governs its work-doing power. 

 But the tension developed also depends upon the length 



A B 



a 



A. 



Fig. 124. — Influence of the length of a Muscle upon the work done. A is 

 a muscle of two inches, and in contracting to half its length it lifts a 

 weight to one inch. B is a muscle of one inch. It lifts the weight to 

 half an inch. 



of the muscle at the moment of stimulation (p. 224); this 

 and every factor which influences the force of muscular 

 contraction also influences the work which can be done (see 

 p. 245 et seq.). 



One factor, the eftect of the load, requires special con- 

 sideration. It has already been shown that as this is increased 

 the lift or extent of contraction is diminished. 



The following experiment, represented in fig. 1 25, illustrates 

 the influence of increasing the load on the work-doing power 

 of a muscle — 



A 



Fig. 125.- 



-To show the influence of Load on the Work done. 



Load. 



Lift. 



— — — — Work. 



It will be seen that increasing the load at first increases the 

 amount of work done, but that, after a certain weight is 

 reached, it diminishes it. There is, therefore, for every 



