234 



PRACTICAL PHYSIOLOGY. 



[XLV. 



the level of the U-shaped tube, 

 two corresponding kaolin caps. 



The muscle is placed on the 



3. Shunt. This is an arrangement by which a greater or less 

 proportion of a current can be sent through the galvanometer (fig. 

 158). The brass bars on the upper surface 

 are marked with the numbers ^, -$\, T ^ , 

 indicating the ratio between their resistance 

 and that of the galvanometer, so that when 

 the plug is inserted in the several positions, 

 yV> T07r> or TTTOIF f tne whole current may be 

 sent through the galvanometer. 



4. Muscle Demarcation-Current (Current 

 of Injury). 



(a.) Arrange the apparatus according to the 

 scheme (fig. 159). 



(b.) Place a shunt between the N.P. elec- 

 FIG. 1 5 8.- The shunt. trodes and the galvanometer. Connect two 

 wires from the electrodes to the binding 

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

 attach two wires to the galvanometer. Insert a plug (C) between 



Fid. 159. Arrangement of Apparatus for the Demarcation-Current of Muscle. M. Muscle 

 on a glass plate, P ; S. Shunt ; G. Galvanometer ; Mg. Its magnet moved by the 

 milled head, in; L. and Sc. Lamp and scale. 



A and B, thus short-circuiting the muscle-current. When work- 

 ing with muscle, keep a plug in the hole opposite on the 

 shunt. Arrange the lamp and scale so as to have a good image of 



