40 LABORATORY MANUAL OF GENERAL PHYSIOLOGY 



to cathode? Observe with a reading glass. Cf. Loeb, "Forced 

 Movements," p. 44. Text p. 331. 



IX. MUSCULAR MOVEMENT AND NERVOUS ACTION 



APPARATUS 



Precautions. — Handle all equipment with great care. Keep metal 

 parts free from salt solution (especially muscle levers). Avoid scratching 

 drum when removing kymograph paper. Do not bend tips of electrodes. 

 Smoke drums lightly. Students who have not received adequate training 

 in physics should read "Physical Principles of Electricity and Magnet- 

 ism" by R. W. Pohl (trans, by W. M. Deans) 1930. 



1. Electrolysis. — Apply two wires connected to a dry cell to neutral 

 litmus paper moistened with NaCl solution (or Ringer). Note reactions 

 at anode (positive) and cathode (negative). Apply also to filter paper 

 moistened with starch solution containing KI. Explain result. 



2. Induction Coil. — Wires of two circuits are arranged in parallel 

 coils — primary circuit (inducing) and secondary circuit. When current 

 is made or broken in the primary circuit, or when its intensity is altered, 

 a momentary induced current appears in the secondary circuit. An 

 automatic interrupter is inserted in the primary circuit. Place the 

 primary coil in circuit with a simple key and dry cell. Make a diagram 

 of the instrument, showing its arrangement and connections. The left 

 and centre binding posts are used for single shocks and the outer ones for 

 the interrupter. 



Attach electrode wires to the secondary coil and apply to "pole- 

 finding paper." (Starch plus KI.) Arrange the primary circuit to pro- 

 vide single shocks. Close and open the key a number of times. Result? 

 Repeat, but cross circuit the secondary coil each time before breaking. 

 Result? Repeat, but cross circuit so as to eliminate the "make." 



Separate the two coils by pushing out the secondary. Close the 

 primary circuit and then place the electrodes on the tip of the tongue. 

 Result? Now make and break several times. Result? Slide secondary 

 coil nearer. What is effect on the intensity of the shocks? Is make 

 "stronger" than break? 



3. Pole Changer (Reversing Key, or Rocking Key). — Study its mecha- 

 nism. Draw diagrams showing the connections required for its use (1) 

 to reverse current, (2) as a double key without changing the wires, (3) as 

 a single key. Observe insulated ends of wires (rubber bushing). 



4. Non-polarizable Electrodes. — (Can be supported with plasticine 

 or holder.) These are soaked in Ringer's solution, then filled with ZnS04 

 solution in which a Zn rod is dipped. ZnS04 must not be spilled on the 

 outer surface of the electrodes. Describe the mechanism of current con- 



