GENERAL PHYSIOLOGY OF MUSCLE AND NERVE TISSUE 49 



may thus be readily dissected out. Care should be taken not to 

 stretch, pinch, or cut the nerve during this process. Lay the nerve 

 upon the gastrocnemius muscle. 



(5) Grasp the triceps femoris muscle, pass a blade of the scissors 

 under its tendon; sever, and remove the whole mass of muscles 

 anterior to the femur. In a similar manner remove the muscles 

 posterior to the femur. 



(6) Grasp the tendo Achillis, sever it low down where it passes 

 over the calcaneum, lift up the gastrocnemius and sever the tibia 

 and its associated muscles as near the knee-joint as possible. 



(7) Sever the femur at the juncture of its middle and upper thirds. 

 The finished preparation has the characteristics shown in Fig. 28. 

 A segment of the vertebral column may or may not be left on. 



(6) The Indirect Stimulation of the Gastrocnemius. 



4. Observations. To mount the muscle-nerve preparation in the 

 myograph. Fix the femur in the clamp (Fig. 26, C) ; place a piece 

 of filter paper, wet with normal saline solution, upon the glass nerve- 

 support (S) ; lay the nerve upon the support, make a longitudinal 

 slit in the tendo Achillis, pass the hook of the muscle lever through 

 the slit, and so adjust the height of the clamp as to bring the lever 

 into a horizontal position. 



(a) Mechanical Stimulation. (1) Snip off with the scissors the 

 central end of the sciatic nerve. If the muscle instantly contracts, 

 thereby lifting the lever, the observer will know that his preparation 

 is successful. If it does not respond to the first stimulation it may 

 to a second or subsequent one. If it responds to later stimuli, but 

 not to the first ones, one may conclude that in making the prepara- 

 tion a portion of the central end of the nerve was killed. 



(2) What may one conclude if the muscle responds to stimuli 

 applied to a central end of the sciatic nerve, but later fails to respond 

 to stimuli applied farther along the course of the nerve i. e., nearer 

 the muscle? 



(6) Thermal Stimulation. Make and mount a fresh preparation. 

 Heat the copper wire in a gas flame and touch the end of the nerve 

 with the hot wire. If the preparation has been successful the muscle 

 will respond by a contraction. If the preparation is a good one, 

 save at least two-thirds of the nerve for the subsequent experiment. 



(c) Chemical Stimulation. Cut off the part of the nerve which is 

 dead and lay the central end of the still functional nerve in a saturated 

 solution of common salt. Await results. Record all results. 



(d) Electric Stimulation. While in the operation of making -a 

 gastrocnemius preparation after the sciatic nerve has been freed from 

 the other structures in the thigh, slip the glass nerve hook under it 

 so that the handle of the nerve hook will hold the nerve away from 



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