334 TRESENT STATE OF ORGANIC ELECTRICITY. 



induces contraction, and of a sensory nerve while it is convey- 

 ing to the sensorium the impression produced at its peripheral 

 extremity. In this investigation it was necessary to produce 

 in the nerve that state of continuous activity which is required 

 for overcoming the inertia of the needle. Such a condition 

 may be procured by mechanical or chemical agents, or by the 

 transmission of interrupted electric currents. 



A segment of a nerve having been placed so that its longi- 

 tudinal and one of its transverse sections are in connection 

 with the electrodes of the galvanometer, if, after the needle 

 has come to rest at the angle of deflection produced by the 

 nerve-current, tlie other end of the nerve be burned or crushed, 

 the needle will return towards zero a few degrees. 



If the extremity of the nerve of a rheoscopic leg be con- 

 nected with the galvanometer in a similar manner, and the 

 leg itself be confined in one limb of a glass syphon, into which 

 a boiling solution of salt is passed from the opposite limb, the 

 needle will indicate a similar negative variation. 



A frog having been fastened down, its sciatic nerve laid 

 bare, cut across at the lower end, and turned up from the 

 thigh, so as to have its longitudinal and transverse sections 

 applied to the electrodes, the needle will exhibit the usual 

 positive deflection. If tlie animal be now tetanised by strych- 

 nine, tlie needle wiU return towards zero, and continue to 

 oscillate, approaching zero during each spasm, and receding 

 from it in the intervals of muscular action — that is, while the 

 nerves are not engaged in conveying their stimulus of muscular 

 contraction. 



Erom these experiments it appears, that when a motor or 

 sensory nerve is in a state of functional activity, its ordinary 

 electric condition is altered, as it no longer affords the same 

 galvanometric indications, the current derived from it being 

 diminished. 



Electricity passed through a nerve excites that condition 



