LESSON V. POLAR STIMULATION. FATIGUE. 



1. Make the following preparations from a pithed 

 frog, and place them in saline solution: 



a. Rectus abdominis preparation. Remove the 

 skin over the abdomen. The two rectus abdominis 

 muscles will be seen one on either side of the mid-line 

 arising from the sternum and ending in a point at the 

 pelvis. Note that it is divided into segments by trans- 

 verse tendinous insertions (cf. Fig. 16). Cut through 

 the xiphisternum transversely, and, taking this in for- 

 ceps, cut out the rectus muscle of one (or both) sides. 



b. Two sciatic-gastrocnemius preparations. 



2. Polar stimulation in muscle. Connect the ac- 

 cumulator with a battery giving a current of about 



Fig. 15. A accumulator. K in-circuit key. P potentiometer. S 

 slider. C commutator. E electrodes with muscle pinned across 

 them. 



4 volts with a potentiometer, a commutator (reversing 

 key) and electrodes as in Fig. 15. (With a current of 



