78 



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 contact is 

 made ? This is known as Galvani's experiment. 



309. 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 care- 

 fully in such a way that its cross-section 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 demar- 

 cation currents. 



XXI 



310. Induction Machine or Inductorium. Principle 

 of action : If portions of the wires forming two separate cir- 



FIG. 11 



Fig. 11, Induction coil, ab, binding posts for single induced currents ; cd, 

 binding posts for interrupted currents ; e, post connecting Neef's hammer with 

 the primary coil ; /, electro-magnet ; p, primary coil ; s, secondary coil. 



