54 LABORATORY MANUAL OF GENERAL PHYSIOLOGY 



skeletal muscle and loops of earthworm (cf. Bayliss, pp. 436-37). Earth 

 worms may be used for this experiment. Text p. 289. 



23. Microscopic Study of All-or-None Effect in Skeletal Muscle. — 

 Carefully remove a sartorius muscle. Place in Petri dish. Fasten down 

 one end firmly with a pin passing through a cork attached to rim of dish 

 (see demonstration). Similarly fasten down the other end with a needle 

 covered with wax except at extreme tip. Determine cathodal post of induc- 

 torium for break shocks (eliminate makes) using starch-KI paper. Wire 

 stimulating needle as cathode. Shake a bottle of charcoal and blow 

 escaping fine dust on muscle. Cover with Ringer into which dip a wire 

 (anode) from other post of inductorium. Observe muscle through 

 microscope and stimulate with break shocks with a mercury key in 

 primary circuit. Find particles that move lengthwise of the muscle. 

 Starting with a just threshold break move secondary coil closer, a mm. 

 at a time, and observe relation between strength of stimulus and move- 

 ment of particles. Compare results when a single fibre is excited and when 

 many fibres are in action. Are effects compatible with the All-or-None 

 Law? (cf. Pratt and Eisenberger, Am. J. Physiol., 49: 1, 1919). For a 

 review of the All-or-None Law, cf. Rosenbleuth, Quart. Rev. Biol., 10: 

 334, 1935; Brown and Sichel, Jl. Cell. Comp. Physiol., 8: 315, 1936. Text 

 p. 299. 



24. Isolation of Impulse Path. — Wire a needle to one post of inductorium 

 arranged for minimal tetanizing currents. Skin the legs of a pithed frog 

 and expose the sacral nerve plexus. With a copper wire "ground" the 

 head (to water or gas pipes) and touch the sacral nerves here and there 

 with the needle electrode and observe effect on sartorius or other muscles. 

 Do all fibres contract? 



25. Does a Nerve Fibre Conduct in Both Directions? — Carefully sever a 

 gracilis muscle at its insertion and turn to reveal inner surface. Note 

 where the nerve and blood vessels divide going to each side of the muscle. 

 Cut muscle in half between the nerve branches. Avoid injury to nerve. 

 Stimulate one half. Does the other half contract? 



26. Reciprocal Inhibition in Crustacean Muscle (Fig. 4). — Remove a 

 leg from a lobster or crab (or claw of crayfish). Note a sequence of flexion 

 and extension produced by stimulus of cutting off the limb. With a 

 probe make holes in the shell on the leg for electrodes (near proximal end). 

 Clamp limb securely so that only the terminal segment (dactylus) is 

 moveable. Plasticine may be used. Attach the dactylus with thread 

 to a heart lever. Irrigate with sea water or Crustacean Ringer solution. 

 Make a base line to distinguish between extension and flexion on the 

 record. Starting with a very weak tetanizing current determine the 

 effect of gradually increasing the strength of stimulus (continuous stimu- 

 lation). The dactylus must be placed in a half way position so that 

 flexion or extension may be recorded. These preparations are very 



