THE MUSCLES. 27 



4. Standing with heels near together, rise on the toes 

 and then sink as far as possible, bending ankles 

 and knees. Repeat six or ten times. Explain. 



F. The Way in which Muscles Act. 



Materials. A frog. Ether. Cotton batting. 



Apparatus. Ring-stand. Small induction coil. Battery. Wires, etc. 



Etherize the frog, cut the spinal cord just back of the 

 head and destroy the brain with a probe. Lay bare the 

 gastrocnemius (calf) muscle in one hind leg with the nerve 

 leading to it (the sciatic nerve), and cut the several branches 

 of this nerve close to the backbone. 



1. Stimulate the nerve, with a single shock, close to the 



backbone and watch results. Does the result 

 follow instantaneously? Why? How long does 

 it take the muscle to recover its normal position ? 



2. Stimulate at any point with a rapid succession of shocks. 



What difference is there in the result? Call this 

 tetanus, and show its relation to convulsions and 

 cramp. How long does it take the muscle to recover? 



3. Expose the muscle and nerve on the other hind leg, 



cut, and repeat 1 and 2 to verify the results before 

 obtained, watching especially the interval which 

 elapses between stimulation and contraction. 



4. Repeat the single shock stimuli many times at quite 



short intervals, allowing the muscle to recover each 

 time. Note the decreasing strength of contraction 

 produced and the increasing length of time it takes 

 to recover. This is fatigue. 



