DEMARCATION CURRENT OF MUSCLE. 



189 



(d.) Into each tube introduce a well amalgamated short 

 piece of zinc wire with a thin copper wire soldered to its 

 upper end (Z, Z), fix the electrodes in suitable holders 

 in a moist chamber, and attach the wires of the zincs to 

 the binding screws in the plate or stage of the 

 moist chamber. 



3. The Brush-Electrodes of v. Fleischl are very 

 convenient. They consist of glass tubes 5 mm. in 

 diameter and 4 cm. long. Into one end is fitted a 

 perfectly clean camel's-hair pencil, and into the 

 other dips a well-amalgamated rod of zinc with a 

 binding screw at its free end. Place some clay in 

 the lower part of the tube, and then fill it with a 

 saturated solution of zinc sulphate. A piece of 

 india-rubber tubing fits as a cap over the upper end 

 of the glass tube. The brushes are moistened with 

 a mixture of kaolin and normal saline. 



4. The Shunt. This is an arrangement by which 

 a greater or less proportion of a current can be 

 sent through the galvanometer (Fig. 81). 



Fig. 80. Non- 

 pol arisable 

 Electrodes. 

 Z, Zincs ; K, 

 cork ; a, zinc 

 sulphate solu- 

 tion ; t, t, clay 

 points. 



The brass bars on the upper surface are 

 marked with the numbers 7^, , 7^77, in- 

 dicating the ratio between their resistance 

 and that of the galvanometer, so that when 

 the plug is inserted in positions afterwards 

 to be mentioned, there may be y 1 ^, -j-J^, or 

 Y^Vo of the whole current sent through the 

 galvanometer. 



5. Demarcation Current of Muscle. 



(a.) Arrange the apparatus accord- 

 ing to the scheme (Fig. 82). 



Fig. 81. The Shunt. 



(b.) Introduce a shunt between the 

 N.P. electrodes and the galvanometer. 

 Connect two wires from the electrodes to the binding screws 

 (A and B) of the shunt, and from the same binding screws 

 attach two wires of the same kind to the galvanometer. 

 Insert a plug (0) between A and B, whereby the muscle 



