242 PHYSIOLOGY OF MUSCLES AND NERVES. 



non-magnetic iron may at any time be transformed into 

 a magnet, makes the involved conception quite natural. 

 It is exactly the same in the case of the electric organs 

 of the torpedo. The fact that they, though in them- 

 selves electrically inoperative, become electrically oper- 

 ative under the influence of the nerves, when combined 

 with what we know of nerves and m.uscle, naturally 

 leads us to suppose that electromotive forces are pre- 

 sent in the electric plates, but that they are so ar- 

 ranofed as to cause no observable differences of tension 

 on the outer surface. Under the influence of the ac- 

 tive nerves, the particles endowed with electric forces 

 undergo a change in their relative position, differences 

 of tension between the two surfaces of the electric plates 

 intervene, and, as all the electric plates in an organ act 

 in the same way, the result is a powerful electric shock, 

 which, in spite of its powerfid effect, differs from the 

 negative variation of the m.uscle- and nerve-currents only 

 as does the powerful current of a many-celled galvanic 

 battery from the weak current of a small apparatus. 



In order to make the similarity between the electric 

 organ on the one hand, and muscles and nerves on the 

 other, yet more prominent, we w^ill carry the compari- 

 son with magnetic phenomena yet further. In fig. 65, 



B N s 



Fig. Go. IVLvgxktio im)L'<ti(»x. 



J. j5 is a piece of soft iron, N S a magnet which we bring 

 from some distance toward the iron rod A B. The result 

 is to evoke magnetism in J. J5, J. becoming a north pole, 

 and B a south pole. Now^, let us suppose that the non- 

 magnetic iron rod AB i?> replaced by an entirely similar, 



