164 



PRACTICAL PHYSIOLOGY. 



[xxvr. 



(c.) Make a table showing the extent of deflection of the needle 

 of the detector according to the distance of S from "W. 



11. The wire of the rheochord may be arranged as in fig. 91 ; 

 a slider, S, S, consisting of an ebonite cup filled with mercury, 

 can be moved along the wires. Make connections as in fig. 91. 

 Observe as the mercury cup is pulled away from the binding 



FIG. 91. Rheochord with Hg-Slider, S. S. B. Battery ; K. Contact Spring-Key ; 

 E. Electrodes ; N. Nerve or Detector. 



screws there is a greater deflection of the needle, but the deflection 

 is not in proportion to the distance of the cup. Make a table of 

 your results. 



The resistance in the rheochord circuit is low as compared with 

 that in the principal circuit. By means of the slider the resistance 

 in the deriving circuit can be increased or diminished, and, con- 

 sequently, the magnitude of the current diverted into the principal 

 circuit. The rheochord also affords a means of dividing a current 

 into two parts, according to the respective resistances in the 

 two circuits. A rheochord is also used to compensate any current 

 of injury in nerve and muscle in rheotonic experiments. 



12. Simple Rheochord. The most convenient form is that 

 shown in fig. 92, and is that used in the Physiological Laboratory 



