MUSCLE 



537 



FIG. 150. ASTATIC PAIR 

 OF MAGNETS. 



FIG. 152. COMPENSATOR. 



FIG. 151. DIAGRAM OF RHEOCORD 

 (AFTER Du Bois - REYMOND'S 

 MODEL). 



Description of Fig. 150. SN and NS are the magnets, fixed to the vertical piece P. 

 M is a mirror. The arrow-heads show the direction of a current which deflects both 

 magnets in the same direction. 



Description of Fig. 151. I. to VII. are pieces of brass connected with the wires 

 a to/ in such a way that by taking out any of the brass plugs i to 5, a greater or Jess 

 resistance may be interposed between the binding screws A and B. The two wires a 

 are connected by a slider s, filled with mercury or otherwise making contact between 

 the wires. The current from the battery B' divides at A and B, part of it passing 

 through the rheocord, part through N, the nerve, muscle, or other conductor which 

 forms the alternative circuit. When a sufficient resistance R is interposed in the chief 

 circuit to make the total strength of the current independent of changes in the 

 resistance of the rheocord, the strength of the current passing through N will vary 

 inversely as the resistance of the rheocord. When all the plugs are in, and the slider 

 close up to A, there is practically no resistance in the rheocord, and all the current 

 passes across the brass pieces and plugs to B, and thence back to the battery. As s is 

 moved further away from A, the resistance of the rheocord is increased more and 

 more, and the intensity of the current passing through N becomes greater and greater. 

 The scale S shows the length of wire interposed for any position of s, and this gives a 

 rough measure of the fraction of the current passing through N. When plug i or 2 is 

 taken out, a resistance equal to that of the two wires a is interposed ; plug 3, twice that 

 of a t - plug 4, five times ; plug 5, ten times. 



Description of Fig. 152. W is a wire stretched alongside a scale S. A battery B is 

 connected to the binding screws at the ends of the wire. A pair of unpolarizable electrodes 

 are connected, one with a slider moving on a wire, the other through a galvanometer 

 with one of the terminal binding screws. In the figure a nerve is shown on the elec- 

 trodes, one of which is in contact with an uninjured portion, the other with an injured 

 part. The slider is moved until the twig of the compensating current just balances the 

 demarcation current of the nerve and the galvanometer shows no deflection. 



