10 



PRACTICAL PHYSIOLOGY 



shall pass through the experimental circuit. It 

 usually consists of a german-silver or platinum- 

 iridium wire of a certain known resistance (e.g., 



FIG. 14. POHL'S COMMUTATOR USED AS SWITCH (CROSS WIRES REMOVED). 



20 ohms), to the ends (Fig. 15, a and b) of which 

 the battery poles are connected ; a certain differ- 

 ence of potential is thereby produced at the two 



FIG. 15. DIAGRAM OF RHEOCHORD. 



ends of the wire. With one of these ends (a) an- 

 other wire is connected ; this forms part of the ex- 

 perimental circuit through which a portion of the 

 battery current is to be conducted ; this circuit is 



