THE REFLECTING GALVANOMETER 



149 



By a somewhat similar experiment one muscle may be directly 

 stimulated by the current of action of another. Thus if two sartorius 

 preparations be made from a curarised frog and the one muscle 

 pressed tightly against the other, so that at each end one of the 

 muscles projects a little, tetanisation of one muscle at its uncovered 

 end leads to a tetanus of the second. 



Experiment 5. — Show the current of action of the heart by excising the 

 whole heart, and having nearly emptied it of blood by touching it with dry 

 blotting-paper, injure the apex of the ventricle and then place it on a 

 thoroughly dried glass plate. Dissect out a sciatic very carefully and with 

 the leg still attached place it on the heart, so that it crosses the base of the 

 ventricle and its cut end lies on the injured spot at the apex of the heart. 

 With each contraction of the heart the muscles of the leg give a single 

 twitch, being stimulated by the current of action of the heart. 



Apply a Stannius ligature to the heart, which is thus brought to a stand- 

 still. With each mechanical stimulation the ventricle gives a beat and its 

 current of action leads to a twitch of the leg muscles. 



II. EXAMINATION OF THE DIFFERENT CURRENTS BY 

 MEANS OF THE REFLECTING GALVANOMETER 



The galvanometer employed for this purpose consists of a pair of 

 suspended magnets which are made very nearly astatic, each being 

 surrounded by a coil consisting of very many turns of fine insulated 

 wire. 



Galvanometer. Shunt. Lamp and Scale. 



Fig. 118. — Side View of Galvanometer and Shunt, Lamp and Scale 



The galvanometer and scale are placed east and west, and appear as if viewed by an observer 

 standing on the north side and looking south ; the path of light is indicated by dotted lines. The 

 essential parts concealed by the galvanometer case are diagrammatically given in fig. 119. (Waller.) 



The two coils are connected up so that the current is sent clock- 

 wise through one coil, and anti-clockwise through the other (see 



