12 



EXPERIMENTAL PHYSIOLOGY 



Rheochords. A rheochord is an apparatus for dividing a constant 

 current by offering a circuit of relatively small resistance which is 

 capable of being varied so that a variable part only of the current 



FIG. 18. Diagram of Malcolm's commutator. 



FIG. 19. Diagram of rheochord. 



shall pass through the experimental circuit. It usually consists of a 

 ger man- silver or platinum-iridium wire of a certain known resistance 

 (e.g., 20 ohms), to the ends (Fig. 19, a and b) of which the wires from 

 a cell are connected ; a certain difference of potential is thereby pro 



