SHERRINGTON DRUM 23 



the figure. Take the pulleys in the right hand (if the 

 machinery is in motion, the pulleys must be prevented 

 from rotating), loosen the screw 8, lift up the catch by 

 the button G, and push in the pulleys. On the projecting 

 pulley shaft Sh will be seen three grooves, when the 

 catch is in the innermost groove the fast gear is engaged, 

 when it is the outermost groove the slow gear is engaged ; 

 when it is in the middle groove the gearing is disengaged. 

 Fix the catch in each groove in succession ; after fixing, 

 release the pulley, turn the handle H and note the effects. 

 In place of a knock-down key, there is a projection on 

 the inner side of K, which when pushed in by the arm 

 on the drum shaft makes contact with the two binding 

 screws on K. One end of K is moveable, so that the 

 projection can be taken out of range of the arm. 



2. Tracing of a single muscular contraction. 



a. Connect the cell with the primary coil of the in- 

 ductorium, interposing the knock-down key as an in- 

 circuit key (cp. Fig. 7). Connect the secondary coil with 

 a short-circuit key, and this with the binding screws 

 connected with the electrodes (H, H) of the muscle 

 chamber (Fig. 10). 



Adjust the heights of the drum and of the muscle 

 chamber so that the lever G when horizontal is a few 

 centimetres above the lower edge of the drum and can 

 be brought nearly to the level of the upper edge by 

 lowering the drum. 



6. The nerve muscle preparation. Take a pithed 

 frog and cut through the skin all round the animal at 

 the middle of the trunk, turn the edge of the skin down- 

 ward, and seizing it with a cloth, tear the skin from the 

 lower half of the trunk as far as the knee. On a glass or 



