MUSCLE 



5*7 



some extent recover, and be again able to contract, although 

 exhaustion is now more readily induced than at first. 



What is the cause of muscular fatigue ? An exact answer 

 is not possible in the present state of our knowledge, but 

 we may fairly conclude that in an isolated preparation it is 

 twofold : (i) The material necessary for contraction breaks 

 down more quickly than it can be reproduced or brought 

 to the place where it is required; (2) waste praJucts are 



FIG. 175. FATIGUE CURVE OF SKELETAL MUSCLE 



(Gastrocnemius of frog, indirect stimulation), taken with arrangement shown in 

 Fig. 192. Time-tracing, TSS of a second. 



formed by the active muscle faster than they can be removed. 

 That even an isolated muscle has a certain store of the 

 material needed for contraction which cannot be all exhausted 

 at once, or which can to a certain extent be replenished by 

 processes going on in the muscle, is shown by the beneficial 

 effect of mere rest. That the accumulation of fatigue 

 products has something to do with the exhaustion is shown 

 by the fact that the muscles of a frog, exhausted in spite of 

 the continuance of the circulation, can be restored by bleed- 



