50 ADVANCED LESSONS IN PRACTICAL PHYSIOLOGY 



Annotation. If this muscle possesses a high degree of irritability, increase the 

 number of the contractions between the successive records. Since a very responsive 

 muscle may contract as many as 750 times against a weight of 20 grams before it 

 is fatigued, the differences between the successive contractions might not be suf- 

 ficiently evident unless some such procedure is followed to hasten the onset of fatigue. 

 Naturally, fatigue may also be brought on more quickly by increasing the weight 

 lifted by the muscle. As has been stated above, the writing lever should not be 

 removed from the smoked paper, because this alters the friction and interferes with 

 the steady decline and lengthening of the successive curves. 



Use the other gastrocnemius muscle of the same frog and attach it 

 to the recording apparatus. Arrange the electric apparatus for stimula- 

 tion with a quickly interrupted current (posts 1 and 3 of the induc- 

 torium). Upon a slowly revolving drum record a tetanic contraction 

 lasting twenty seconds. Directly underneath record a second contrac- 

 tion of equal duration, and underneath this one, a third and fourth, 

 until the muscle has been fatigued. 



