42 LABORATORY MANUAL OF GENERAL PHYSIOLOGY 



duction when these are applied to a tissue. Place litmus paper moistened 

 with Ringer across the electrodes. Wire zincs to a dry cell. 



Does electrolysis occur? Wash out the ZnS04 solution and dry the 

 Zn rods. Place the electrodes in Ringer solution until needed again. 

 Compare other types of non-polarizable electrodes (cf. Mitchell, "General 

 Physiology," 1932, p. 21). 



5. Kymograph. — Examine muscle levers, writing levers, signal mag- 

 nets, femur clamp, tuning fork (electrical). These instruments require 

 extremely delicate manipulation. The writing levers, mounted on a 

 stand on the right, must be tangential to the drum. In every experiment 

 set up the apparatus before making the dissection. 



MUSCLE CONTRACTION 



Striated muscle is characterized histologically by a double helicoid or 

 spiral which appears as striations when viewed from the side (cf. Tiegs, 

 Proc. Roy. Soc. B, 116: 38, 1934). Examine and draw a common test tube 

 brush as a good example of a double helicoid. Text p. 291. 



Nerve Muscle Preparation. — Destroy brain and spinal cord of a frog 

 by pithing with a nail (as demonstrated). Remove skin from the frog 

 (except from the head); skin secretions injure the muscles and nerves (cf. 

 Szabuniewicz, Pfliigers Arch., 223: 744, 1930). Note on dorsal thigh 

 surface a longitudinal depression between vastus externus and semimem- 

 branosus muscles. The sciatic nerve lies in this groove, with blood 

 vessels. Lift it gently, and isolate it as far as the knee. Then separate 

 the thigh muscles with forceps and follow the nerve toward the spinal 

 cord. Avoid putting traction on the nerve. Tie a moistened silk thread 

 on the proximal end of nerve. Cut its roots as near the cord as possible. 

 Cut the femur through the middle and remove the thick muscles. Tie a 

 thread on Achilles' tendon. Cut the tendon of Achilles below the ankle. 

 Lift the gastrocnemius muscle from the leg and cut through bone just 

 below the knee. The preparation must be moistened constantly with 

 Ringer. 



Fix cut end of femur in a femur clamp and lay the nerve on a glass slide 

 or across the electrodes. 



1. Efficiency of Make and Break Shocks. — With 2 dry cells in circuit 

 use inductorium for single shocks (left and center terminals). Attach 

 the muscle to muscle lever for writing on kymograph. Arrange with 

 great care to give muscle full mechanical advantage. Mark a base line. 

 On a stationary drum record the height of contraction elicited by make 

 (closing) and break (opening) shocks. Carefully label the records M 

 or B. Move the drum 5 mm. between records. If no contraction occurs 

 indicate by a short line beneath the base line. The make shocks are 



