GENERAL PHYSIOLOGY OF MUSCLE AND NERVE TISSUE 39 



(c) The Pole Changer or Commutator. Most convenient for the 

 physiological laboratory is PohPs commutator (Fig. 14). This in- 

 strument may be used for the following purposes: 



FIG. 15 



FIG. 16 



FIG. 18 



^===^~Tnrrr-^--r-^rrf^^ 



\z^2~^ i ~^ Ji ^^ 



FIG. 19 



(1) To change the direction of the current. Set up apparatus 

 with cross-bars in place as shown in Fig. 17. Which is the anode 

 when the bridge is turned toward a b f Which is the anode when 

 the bridge is turned toward c d? 



