234 



PRACTICAL PHYSIOLOGY. 



[XLY. 



the level of the (J -shaped tube. The muscle is placed on the 

 two corresponding kaolin caps. 



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

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

 158). The brass bars on the upper surface 

 are marked with the numbers -g-, -^V, -g-^y^, 

 indicating the ratio between their resistance 

 and that of the galvanometer, so that when 

 the plug is inserted in the several positions, 



tV, 



ToTTj 



or 



000 



of the 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- 

 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 



FlO. 158.- The Shunt. 



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

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

 miUed head, m; 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 



