XLVII.] 



GALVANIS EXPERIMENT. 



239 



LESSOK XLVIL 



GALVANI'S EXPERIMENT— SECONDARY CONTRAC- 

 TION AND TETANUS — PARADOXICAL CON- 

 TRACTION— KtTHNE'S EXPERIMENTS. 



1. Galvani's Experiment. 



(a.) Destroy the brain of a frog, divide tke spine aboi>t tlie 

 middle of the dorsal region, cut away the upper part of the body, 

 and remove the viscera. Remove the skin from the hind-legs, divide 

 the iliac bones and urostyle, avoid injuring the lumbar plexus, 

 which will remain as the only tissue con- 

 necting the lower end of the vertebral 

 column with the legs. Thrust an S-shaped 

 copper hook through the lower end of the 

 spine and spinal cord (fig. 163). 



(b.) Hook the frog to an iron tripod. 

 Tilt the tripod so that the legs come in 

 contact with one of the legs of the tripod ; 

 vigorous contractions occur whenever the 

 frog's legs touch the tripod. 



(c.) With the frog hanging perpendicu- 

 larly without touching the tripod, make a 

 U-shaped piece of wire composed of a 

 copper and zinc wire soldered together. 

 Touch the nerves above with the copper 

 (or zinc) end, and the muscles below with 

 the zinc (or copper), when contraction occurs at make, or break, 

 or both. 



Fig. 163.— Galvani's 

 Experiment. 



2. Contraction without Metals. 



(a.) Make a fresh nerve-muscle preparation, leaving the leg 

 attached to the femur, and having the sciatic nerve as long as possible. 

 Hold the femur in one hand, lift the nerve on a camel's-hair pencil or 

 glass rod moistened with normal sahne, and allow it to fall upon the 

 gastrocnemius, when the muscle will contract. Contraction occurs 

 because the nerve is suddenly stimulated, owing to the surface of 

 the muscle having different potential-s. 



{/>.) Or remove the skin from the hind legs of a frog, and dissect 

 out the sciatic nerve in its whole extent. Divide it at its upper 

 end. If the nerve be lifted on a glass rod and allowed to fall 

 longitudinally on the triceps muscle there is no contraction. 



