7 2 4 THE PHYSIOLOGY OF THE CONTRACTILE TISSUES 



relaxation becomes more and more difficult and imperfect (Fig. 279, 

 p. 787) . In smooth muscle (cat 's bladder or ring from frog's stomach) 

 fatigue can be very easily demon- 

 strated in the same way, and the 

 curves present similar features, with 

 the exception that, instead of be- 

 coming longer in fatigue, the suc- 

 cessive contractions become shorter. 

 It is by no means so easy to 

 fatigue a muscle still in connection 

 with the circulation as an isolated 

 muscle. But even the latter, if left 

 to itself, will to some extent re- 

 cover, and be again able to con- 

 tract, although exhaustion is now 

 more readily induced than at first. 



Fig. 251. Fatigue Curve of Muscle-. 

 Frog's Gastrocnemius. The arrange- 

 ment with which the curve figured 

 was obtained was a so-called auto- 

 matic muscle interrupter (Fig. 250). 

 A wire on the lever is made to close 

 and open the primary circuit of an 

 inductorium, the muscle or nerve 

 being connected with the secondary. 

 Every time the needle touches the 

 mercury the muscle is stimulated 

 automatically. 



Fig. 250. Automatic Muscle Interrupter. 

 K, battery; P, primary; S, secondary coil; 

 A, axis of lever; N, needle; Hg, mercury 

 cup. 



In man, muscular fatigue can be studied by means of an arrange- 

 ment called an ergograph (Fig. 255). A record of successive con- 



tig. 252. Fatigue Curve taken on a Slowly-moving Drum (reduced to Half): Frog's 

 Gastrocnemius. Excited through the sciatic nerve by maximal shocks once in 

 six seconds. 



