VOLUNTARY MUSCLE. 15 



Although we are most interested in the physiology of mam- 

 malian muscle, we employ muscles from cold-blooded animals 

 because, while similar in function, they survive for a much longer 

 period when deprived of their circulation. 



Experiment 2. Nerve -Muscle Preparation. Kill a frog in the 

 following manner: By bending the frog's head down, a depression 

 between the skull and first vertebra can be felt on sliding a 

 blunt-pointed seeker back along the mid-line of the top of the 

 skull. Make a short traverse cut in the skin at this point. 

 Plunge a seeker or pithing wire into this depression and turning 

 the instrument forward into the skull cavity destroy the brain. 

 Next destroy the cord by passing the seeker down into the 

 spinal cord. If the frog is properly pithed it immediately 

 becomes limp. Later the muscles may become less flaccid. A 

 frog thus prepared is dead although the heart and other tissues 

 may live for a few hours. There can be no pain whatsoever. 

 This method of killing a frog is called "pithing". 



Slit the skin around a pithed frog just behind its fore legs 

 and remove the skin from the posterior half of the animal. 

 Lay the preparation ventral down on a clean glass plate and 

 keep it moistened with 0.7% salt solution. Carefully dissect 

 out the sciatic nerve on one side by separating the muscles on 

 the dorsal aspect of the thigh and freeing 'the nerve from the 

 surrounding tissues. Always lift the nerve with a glass hook 

 and avoid stretching it. Trace the nerve to its exit from the 

 spinal column. Split the spinal column in two at this point. 

 Leave parts of two or three vertebrae attached to the nerve 

 to serve as a convenient way of handling the nerve and cut 

 the remaining tissue away. 



By means of the vertebrae raise the roots of the sciatic nerve 

 and clip beneath it until it is free down to the knee. Cut the 

 Tendo Achilles and separate the gastrocnemius from the other 

 muscles as far as the knee. Cut the other muscles and the 

 tibia-fibula just below the knee. Cut away all the muscles 

 above the knee and the femur, leaving about half an inch of bone. 

 In making a nerve-muscle preparation one must always 

 remember that slight injury to muscle or nerve may ruin it 

 for experimental purposes. Such injury may be caused by 



