ELECTRIC ORGANS OF FISHES. 217 



powerful shocks were received when one hand grasped the head and 

 the other hand the tail of the Gymnotus, I had painful experience ; 

 especially at the wrists, the elbows and across the back. But our 

 distinguished experimenter showed us that the nearer the hands 

 were together within certain limits, the less powerful was the shock. 

 He demonstrated by the galvanometer that the direction of the 

 electric current was always from the anterior parts of the animal to 

 the posterior parts, and that the person touching the fish with both 

 hands received only the discharge of the parts of the organs included 

 between the points of contact. Needles were converted into mag- 

 nets : iodine was obtained by polar decomposition of iodide of po- 

 tassium ; and, availing himself of this test, Professor Fai'aday showed 

 that any given part of the organ is negative to other parts before it, 

 and positive to such as are behind it. Finally, heat was evolved, 

 and the electric spark obtained. Referring to the admirable Me- 

 moir *, in which these and other experiments on the Gymnotus 

 are described, I shall only revert to the relation which exists between 

 the comparative anatomy of the organs of the Torpedo and Gym- 

 notus, and the diiFerence in the direction of their electric currents, 

 as determined by the physical experiments. The delicate plates sus- 

 taining the terminal meshes of the nerves and vessels are horizontal 

 in the Torpedo ; the course of the electric current is from above 

 downwards. The corresponding plates in the Gymnotus are vertical ; 

 the direction of the electric current is from before backwards : i. c. 

 it is vertical to the planes of the plates of the organised voltaic piles 

 in both cases. 



There is another analogy which the row of compressed cells con- 

 stituting the electric prism of the Torpedo suggests, viz. to the 

 striated fibre of voluntary muscle, or to the row of microscopic discoid 

 cells of which the elementary muscular filament appears to consist. 

 The looped termination of the exciting nerve is common to muscular 

 tissue and that of the electric organ. The electric, like the motory 

 nerves, rise from the anterior myelonal tracts ; and, though they have 

 a special lobe at their origin, beyond that origin they have no ganglion. 

 An impression on any part of the body of the Torpedo is carried by 

 the sensoi'y nerves either directly, or through the posterior myelonal 

 tracts, to the brain, excites there the act of volition, which is conveyed 

 along the electric nerves to the organs and produces the shock : 

 in muscular contraction, the impression and volition take the same 

 course to the muscular fibres. If the electric nerves are divided at 

 their origin from the brain the course of the stimulus is interrupted, 



* LXXXII. 



