XXX.] 



NERVE-MUSCLE PREPARATION, ETC. 



181 



with its belly downwards. With one blade of a sharp-pointed pair of scissors 

 transfix the body immediately behind the shoulder-blades, and divide the 

 spinal column. The head now hangs down, and by its weight it pulls the 

 ventral from the dorsal^ parts. 



(6.) With the scissors divide the wall of the abdomen on both sides parallel 

 to the vertebral column, and remove the abdominal viscera. With the left 

 hand seize the upper end of the divided spinal column, and with the right the 

 skin covering it, and pull. The lower end of the trunk and the lower limbs 

 are denuded of skin. 



(c.) Take the thigh muscles between the thumb and forefinger of the left 

 hand, and with the point of one blade of a pair of scissors tear through the 

 fascia between the biceps and semi-membranosus to expose the sciatic nerve, 

 and then proceed as directed in 1. 



2. Stimuli may be classified as follows : 

 (i.) Mechanical, e.g., cutting or pinching a nerve or muscle. 

 (2.) Chemical, e.g., by dipping the end of a nerve in a saturated 

 solution of common salt or glycerin. 



(3.) Thermal, e.g., applying the end of a heated wire to the 



nerve. 



(4.) Electrical- 



((a.) 

 -(b.) 



Continuous current. 

 Single induction shocks, 

 (c.) Interrupted current or repeated shocks. 



3. Stimulation of Muscle and Nerve. It is convenient to 

 modify somewhat the physiological limb, in order to render the 

 muscular contraction more visible. Apparatus. Seeker, scalpel, 

 scissors, forceps, straw flag, pins, muscle- forceps, camel's-hair brush, 

 saturated solution of common salt in a glass thimble, ammonia, 

 copper wire, spirit lamp or gas-flame. 



4. Mechanical Stimulation. 



('/.) Destroy the brain and spinal cord of a frog (Lesson XXX. 1). 

 Prepare a nerve-muscle preparation, isolat- 

 ing the sciatic nerve, but modify the sub- 

 sequent details as follows : 



(/>.) After the nerve is cleared as far 

 as the spine, clear the muscles away from 

 the femur, and divide the latter about 

 its middle. Divide the sciatic nerve as 

 high up as possible. Pin a straw flag to 

 the toes by means of two pins. Fix the 

 femur in a clamp or pair of muscle-forceps, 

 supported on a stand (fisr. 108), taking care FIG. 108. straw Flag attached 



. a . ' i rm to a Frog's Leg fixed in a 



that the gastrocnemms is upwards. The clamp, ft. Nerve ; F. Flag, 

 nerve hangs down, and must be manipu- 

 lated with a camel's-hair brush dipped in normal saline, or by 

 means of a hooked glass rod. 



