ANIMAL ELECTRICITY. 



89 



about one-sixth of the length of the internal 

 ones. In a fish described by John Hunter,* 

 of which the whole electrical organ was about 

 five inches in length, the longest column was 

 about one inch and a half, and the -shortest 

 about one-fourth of an inch in length. In the 

 same h'sh the average diameter of each column 

 was about two-tenths of an inch. In a fish 

 from the Mediterranean, thirteen inches and a 

 half in length, and about seven inches in 

 breadth, (which, through the kindness of Dr. 

 Allen Thomson, we have had an opportunity 

 of examining in detail,) the length of the 

 longest columns is one inch, and that of the 

 shortest about three-tenths of an inch. Most 

 of these columns are either irregular pentagons, 

 or irregular hexagons ; a few are nearly tetra- 

 gonal. They are united to one another by 

 short but strong fibres, and by a reticular 

 expansion of tendinous threads spread through 

 them. Their number varies considerably ac- 

 cording to the age of the fish. Hunter con- 

 jectured that a few new columns are added 

 every year to the circumference of the organ. 

 In one of the largest fish that has yet been 

 particularly examined, which was four feet and 

 a half in length, the number of columns in 

 one electrical organ was 1182. Mr. Hunter 

 found 470 in each organ in a fish of ordinary 

 size. Mr. Hunter described each column as 

 beinff divided into numerous distinct compart- 

 ments by delicate membranous partitions, 

 placed horizontally, at very short distances 

 from each other. The interstices between them 

 appeared to him to contain a fluid. He found 

 the partitions in several places adhering to one 

 another by bloodvessels; and all, throughout 

 their whole extent, attached to the inside of 

 the column by a fine cellular membrane. In 

 a column of one inch in length, he reckoned 

 150 partitions, and it appeared to him that 

 their number is the same within the same space 

 in all the columns.f Hence, he thought it 

 likely that " the increase in the length of a 

 column, during the growth of the animal, does 

 not enlarge the distance between each partition 

 in proportion to that growth, but that new 

 partitions are formed and added to the extre- 

 mity of the column from the fascia." 



The partitions are covered with fine network 

 of arteries, veins, and nerves. According to 

 Hunter, " they are very vascular." He described 

 the numerous arterial branches which ramify 

 on the walls of the columns as " sending in- 

 wards from the circumference all around, on 

 each partition, small arteries which anastomose 

 upon it, and passing also from one to the other, 

 unite with the vessels of the adjacent parti- 

 tions." The partitions themselves are so deli- 

 cate as not to admit of being satisfactorily 

 examined in the fresh fish : (all Hunter's obser- 

 vations were made upon fish that had been 

 preserved in spirits, by which, doubtless, the 

 delicate membranes were rendered more opaque, 

 and therefore more easily visible.) In point 



* Phil. Trans. 1773, 481. 



t Desmoulins and Majendie say that they found 

 only seven or eight partitions in each column. 

 Anat. des Syst. Nerv. ii. 378. 



of fact, Dr. Davy has never seen them in the 

 course of the numerous dissections which he 

 has made of the electrical organs in fish recently 

 taken ; whereas, in specimens sent hither by 

 him, preserved in spirits, Dr. Allen Thomson 

 and the writer of this article have satisfactorily 

 ascertained their existence and structure as 

 described by Hunter. Dr. Davy says, " when 

 I have examined with a single lens, which 

 magnifies more than 200 times, a column of 

 the electrical organs, it has not exhibited any 

 regular structure ; it has appeared as a homo- 

 geneous mass, with a few fibres passing into it 

 in irregular directions, which were probably 

 nervous fibres."* However, after having im- 

 mersed the organs in boiling water, Dr. Davy 

 has occasionally seen something like a lami- 

 nated structure within the column. Rudolphi 

 satisfied himself of the division of the columns 

 by membranous partitions, and further, that 

 each partition is supplied with a distinct nerve.-f- 

 In a memoir on the comparative anatomy of 

 the Torpedo, Gymnotus, and Silurus, Geoffrey 

 described J the columns as being filled with a 

 semifluid matter composed of gelatine and 

 albumen. 



A large quantity of fluid enters into the 

 composition of the general mass of the elec- 

 trical organs. Dr. Davy has found that they 

 lose more by drying than any other part of the 

 fish nearly 93 per cent. ; while the soft parts 

 in general, including the electrical organs, lose 

 only 84.5 per cent. He believes that the fluids 

 of the organs hold various substances in solution, 

 but the exact nature and proportions of them 

 have not been ascertained. We are indebted 

 to the same indefatigable observer for an ac- 

 count of the specific gravity of the electrical 

 organs. He found it to be very low compared 

 with that of the truly muscular parts of the 

 fish, namely, 1.026, to water as 1.000, while 

 that of a part of the abdominal muscles of the 

 same full-grown fish was 1.058, and of the 

 dorsal muscles 1.065. In a fish eight inches 

 long, five inches across the widest part, and 

 which weighed 2065 grains entire, the electric 

 organs together weighed 302 grains, the liver 

 only 105 grains. 



No contraction has ever been seen in the 

 electrical organs of living fish under the stimu- 

 lus of the strongest excitants, not even under 

 that of galvanism; so that, although what 

 appear to be tendinous threads are spread 

 amongst and over the columns, we have no 

 reason to suppose that any muscular tissue 

 enters into their composition. But, in all 

 directions, they are exposed to the pressure of 



* Phil. Trans. 1832. 259. 



t Abhandl. der Acad. der Wissensch. in Berlin. 

 1820. 224. 



* Ann. du Mus. No. 5. 



The smallest torpedo employed by Dr. Davy 

 in his experiments weighed 410 grains, and con- 

 tained only 48 grains of solid matter; its elec- 

 trical organs weighed 150 grains, and contained 

 only 14 grains of solid matter; yet this small mass 

 gave sharp shocks, converted needles into magnets, 

 affected distinctly the multiplier, and acted as a 

 chemical agent. " A priori, how inconceivable 

 that these effects could be so produced!" 



