34 EXPERIMENTAL PHYSIOLOGY. 



a muscle delays the onset of fatigue and prolongs the staircase 

 effect. 



In frog's muscle fatigue is accompanied by a lengthening of 

 the time for contraction and relaxation, while in mammalian 

 muscle the contractions merely become shorter, with little effect 

 upon the duration. The using-up of materials stored in muscle 

 also contributes to fatigue, for in starvation fatigue is induced 

 more readily while the feeding of glucose helps to prevent it. 



Effect of Fatigue upon Contraction. Fatigue is partially 

 due to the accumulation of waste substances, therefore any re- 

 duction in the circulation will hasten its onset. In the ordinary 

 muscle preparation which has been removed from the circulation, 

 fatigue develops quickly and is easily studied. 



Experiment 13. Pith the brain of a frog taking care to cause as 

 little bleeding as possible. Make a small incision in the skin 

 of the heels and free the gastrocnemius tendons from the ankles. 

 Do not skin the legs. Fasten the frog to the frog board so that 

 the knees are held firmly, but the circulation to the lower legs is 

 not occluded. This may be done by passing a hook through the 

 ligaments on the convexity of the knee. Occlude the circula- 

 tion in the right leg by tying a mass ligature about the thigh 

 and connect the tendon of the right leg by means of a 

 thread to a lever arranged to record contractions of the 

 gastrocnemius. Connect one terminal of the secondary coil 

 to the tendon with a piece of the wire; connect the other 

 terminal to a wire looped about the knee. Arrange to 

 stimulate with maximal make and break shocks. Adjust 

 the after-loading screw and load the muscle with 30 

 grams. Because the first few contractions illustrate important 

 phenomena, do not stimulate the muscle until ready to record 

 the series of contractions resulting in fatigue. 



Start the kymograph revolving slowly and stimulate as 

 uniformly as possible with alternating make and break shocks 

 at second intervals until the muscles cease to respond. Allow the 

 muscle to rest five minutes and record a second fatigue tracing. 

 The record should illustrate the phenomena of (1) Treppe, 

 (2) Fatigue, (3) Contracture. How do you explain Treppe and 

 Fatigue in terms of the All or None law? What change in the 

 behaviour of the muscle is responsible for contracture? 



