Dec. 1, 1866.] 



IIAPDWICKE'S SCIENCE-GOSSIP. 



269 



organs ; aud u the place where the substance is 

 removed. These organs form more than one-third 

 of the whole iish. The two electrical organs are 

 separated at the upper part by the muscles of the 

 back, at the lower part by the middle partition, and 

 by the air-bag at the middle part. 



Fig. 248. 



Fig. 243. 



The electrical organs consist of two parts, viz., 

 flat partitions or septa, and thin plates or mem- 

 branes intersecting them transversely. The septa 

 are thin parallel membranes stretching in the direc- 

 tion of the fish's length, and as broad as the semi- 

 diameter of the animal's body. They vary in 

 length, some of them being as long as the whole 

 body. The very thin plates which intersect the 

 septa have their breadth ecpial to the distance 

 between any two septa. There is a regular series 

 of these plates, from one end of any two septa to 

 the other end, 240 of them occupying a single 

 inch. j 



The electric organ of the Gymnotus depends 

 entirely on its will. It does not keep its organs 

 always charged, and it can direct its action towards 

 the point where it feels itself most strongly irri- 

 tated. When two persons hold hands, and one 

 touches the fish with his free hand, the shock is 

 commonly felt by both at once. Occasionally, how- 

 ever, in the most severe shocks, the person who 



comes into immediate contact with the fish alone 

 receives it. 



A fine specimen of this remarkable fish was for 

 some time in possession of the proprietors of the 

 late Gallery of Practical Science in Adelaide Street, 

 and was made the subject of some interesting expe- 

 riments by Earaday (Ex. Researches, 15th series, 

 1S3S). This fish was 40 inches long. It remained 

 in a healthy aud vigorous condition till March, 

 1842, when it died from the effects of a rupture of a 

 blood-vessel. 



1. The Shock. — This was very powerful when one 

 hand was placed on the body near the head, and the 

 other near the tail. It was like that of a large 

 Leyden battery charged to a low degree ; and great 

 as was the force of a single discharge, the fish was 

 able to give a double and even a triple shock with 

 scarcely a sensible interval of time. Erom some 

 comparative experiments, Earaday thought it may 

 be concluded that a single medium discharge of the 

 iish was at least equal to that of a Leyden battery 

 of fifteen jars, containing 3,500 square inches of 

 glass coated on both sides, and charged to the 

 highest degree. 



2. The Spark. — Through the upper cap of a glass 

 globe a copper wire was passed, a slip of gold leaf 

 being attached to its extremity ; a similar wire 

 terminating in a brass ball within the globe was 

 passed through the lower cap. The gold leaf and 

 brass ball were brought into all but actual contact, 

 the fish being provoked to discharge through the- 

 wires, the gold leaf was attracted to the ball, and a 

 spark passed. 



3. Chemical Decomposition. — Polar decomposition 

 of iodine of potassium was obtained by moistening 

 three or four folds of paper in the solution, and 

 placing them between a platinum plate and the end 

 of a platinum wire, connected respectively with two- 

 saddle conductors grasping the body of the fish. 

 The middle of the fish was found to be negative to 

 the anterior parts, and positive to parts towards the 

 tail. 



4. Magnetic Effects.— By causing the fish to send 

 powerful discharges through an instrument of no 

 great delicacy, a deflection of the needle amounting 

 to 30° was produced ; the deflection was constantly 

 in a given direction, the electric current being 

 always from the anterior parts of the animal, 

 through the galvanometer wire to the posterior 

 parts. When a little helix, containing 22 feet of 

 silked wire wound on a quill, was put into the 

 circuit, and an annealed steel needle placed in the 

 helix, the needle became a magnet, and the direction 

 of its polarity in every case indicated a current from 

 the anterior to the posterior parts of the Gymnotus 

 through the conductors used. 



When a number of persons all dip their hands at 

 the same time into the water in the vessel in which 

 the Gymnotus is confined, they all receive a shock 



