69 



tripod. Tilt the tripod so that the leg may come in contact 

 with one of the iron supports. If the tripod has been 

 painted, scrape the paint off. What happens when the con- 

 tact is made? This is known as Galvani's experiment. 



326. Make another nerve-muscle preparation of the other 

 hind limb, but cut the sciatic nerve as near to the myel as 

 possible and separate the leg from the body at the femoro- 

 pelvic joint. Remove the skin as far as the foot. With 

 the forceps crush the gastrocnemius muscle near the tendon 

 of Achilles. See that the end of the nerve is cut off 

 squarely. With a small brush or thin glass rod lift the 

 nerve very carefully in such a way that its cross-ssection 

 may fall upon the injured portion of the muscle. This 

 stimulates the nerve and causes a contraction of the muscle 

 due to the so-called demarcation currents. 



XXV. 



327. Each student is to have a frog, which is to be pithed 

 and have its brain and myel destroyed by passing a tracer or 

 seeker through the spinal canal. The legs are to be used 

 for nerve muscle preparations. Dissect one leg for the first 

 series of experiments, and reserve the other leg for the sec- 

 ond series. Begin the dissection upon the dorsal aspect of 

 the leg removing the skin and muscles very carefully until 

 the sciatic nerve is exposed. Dissect out the nerve as long 

 as possible, and moisten frequently with the normal salt solu- 

 tion. Remove all of the muscles as far as the knee, leaving 

 the femur and nerve entirely isolated. Avoid all injury to 

 the nerve during dissection, and apply the normal salt .solu- 

 tion every few minutes with a camel's hair brush. Arrange 

 the nerve muscle preparation by placing the femur in a clamp 

 and allowing the nerve to hang freely. A small lever may 

 be pinned to the foot to emphasize any movements that may 

 occur. Apply the following stimuli : 



