CHAP. XI. §. in. THE MAGNETIC NEEDLE. 143 



contact as possible by bending the limb upon the thigh , 

 and the nerve then stimulated at its upper part, but 

 there was no contraction produced in the lower limb. 

 The same conclusion may be drawn, and the same 

 remarks made, in regard to the galvanoscopic frog, 

 as were made in regard to the galvanometer, viz. 

 when the proper precautions were taken, no evidence 

 indicative of the manifestation of cuehent fobce in 

 a nerve ddeing nerve action could be obtained. 



Sect. III. The Magnetic Needle. 



It may be readily supposed, that if we failed to 

 obtain any evidence of the existence of current force 

 in a nerve during nerve action by means of the 

 galvanometer, it would most probably happen that 

 the magnetic needle would also fail to detect it. To 

 exhaust every possible mode of its detection, the 

 following experiments were undertaken. I may just 

 add, that Pbevost', Dumas', and Mullee', have 

 already performed similar experiments, but failed in 

 obtaining any result. 



A small magnetised needle, three quarters of an 

 inch in length, was suspended by means of a single 

 fibre of silk-worm silk, the needle being passed 

 through a strip of card, and to this the silk was 

 attached. To avoid motion of the needle from slight 

 draughts of air, and from vibration of the room, the 

 silk was attached to a firm support, and a glass tube, 

 an inch in diameter and five inches in length, was 

 ' Loc, cit. 



