148 EXPERIMENTAL PHYSIOLOGY. 



LESSON XXVII. 



NERVE-MUSCLE PREPARATION STIMU- 

 LATION OF NERVE MECHANICAL, 

 CHEMICAL, AND THERMAL 

 STIMULI. 



1. Prepare a Nerve-Muscle Preparation Apparatus. A frog, 

 pithing-needle, or " seeker " in handle, iiarrow-bladed scalpel, a 

 small and a large pair of scissors, forceps, towel, and a porcelain 

 plate on which to place the frog. 



(a.) Pith a frog with a pithing-needle, destroying the 

 brain and spinal cord, and place the frog on its belly on a 

 porcelain plate. With the small scissors make an incision 

 through the skin along the back of one thigh say the left 

 from the knee to the lower end of the coccyx, and prolong 

 the incision along the back, a little to the left of the uro- 

 style. Reflect the skin, which is readily done, as there are 

 large lymph sacs between it and the muscles, thus exposing 

 the muscles shown in Fig. 50. 



(6.) Gently separate the semi-membranosus and biceps 

 with the " seeker," and bring into view the sciatic nerve and 

 femoral vessels. Still working with the seeker, and begin- 

 ning near the knee, clear the sciatic nerve of any connective 

 tissue around, but on no account is the nerve to be touched 

 with forceps, nor is it to be scratched or stretched. With 

 the small pair of scissors divide the pyriformis and ilio- 

 coccygeus, and trace the nerve up to the vertebral column. 



(c.) With a sharp-pointed, large pair of scissors divide the 

 spinal column above the seventh lumbar vertebra; seize the 

 tip of the urostyle with forceps, raise it, and with the strong 

 scissors cut it clear from all its connections as far as the last 

 lumbar vertebra, and then divide the urostyle itself. Divide 

 the left iliac bone above and below, and remove it with the 

 muscles attached to it. The lumbar plexus now comes 



