356 GENERAL DIRECTIONS. 



tive (or positive) to those of c. The tilting up of a will then 

 correspond to the making of a current as in Du Bois Rey- 

 inond's key. (See below.) 



XI. Arrangement of Apparatus for Experiment. 

 The electrodes being charged and fastened in their bearers, the 

 bearers secured in the clamps, and the wires from the electrodes 

 brought to the binding-screws of the platform of the moist- 

 chamber, fasten the femur of the nerve-muscle preparation 

 securely in the clamp, in such a way that the muscle* hangs 

 vertically downwards over the slit. Seize the vertebral frag- 

 ment with the forceps, and gently lodge the nerves on the 

 electrodes. Firing fasten the tendo Achillis in a Kronecker's 

 clamp (fig. 274), and with a strong silk thread of appropriate 

 length connect the Kronecker with the lever, the silk passing 

 through the slit. Adjust the arm bearing the muscle, and that 

 bearing the lever, in such a way that the muscle hangs per- 

 fectty vertical, and, without being actually on the stretch, is so 

 attached to the lever (which should be in a perfectly horizontal 

 position) that the slightest contraction of the former will move 

 the latter. 



Bring the wires from the battery, induction coil, etc., to the 

 binding-screws which carry the wires of the electrodes. Place 

 the glass shade over the platform, with wet blotting-paper 

 inside, being careful that the wet paper touches neither the 

 nerve-muscle nor the wires. 



Prepare weights for loading the lever; the most convenient 

 are 5, 10, 20, 30, 50, 150, 200, and 300 grammes. Place the 

 whole apparatus so that the point of the lever touches the 

 registering surface. 



Where it is required to stucty the muscle without removing 

 it from the circulation, another method must be adopted, 

 which may be followed in other cases as well. The upper 

 surface of the platform should in this case be provided with a 

 thick layer of cork. 



Having pithed the frog, pin it firmly, bell}' downwards, on 

 the cork of the platform, fixing the thigh of one side espe- 

 cially tight ; one of the pins should be passed close to the 

 femur, on the anterior surface of the thigh, just above the 

 knee. Make a slight longitudinal slit along the tendo Achillis. 

 which divide low down, and carefully dissect out for a few 

 millimetres; put a small but strong S hook, with a silk thread 

 attached, in the tendon, pass the silk over one of the small 

 double-cone pulleys which are fixed on to the platform, and so 

 through the arms of the T slit to the lever below. 



The sciatic nerve may now be dissected out in the thigh 

 without injuring the bloodvessels, and the curved electrodes 

 slipped beneath it. 



Where the recording cylinder used rotates on its horizontal, 



