Royal Institution of Great Britain. 441 



PROCEEDINGS OF LEARNED SOCIETIES. 



EOYAL INSTITUTION OP GREAT BRITAIN. 



Friday, May 13, 1887. — Henry Pollock, Esq., Treasurer and 

 Vice-President, in the Chair. 



Some Electrical Fishes. By Professor J. S. Bcteddx Sajstderson, 

 M.D., LL.D., F.P.S. 



The lecture was divided into three parts, in the first of which a 

 general description was given of the three most important electrical 

 fish, viz. the torpedo, or electrical ra)^ the electrical eel of the rivers 

 and lakes of South America, and the Mcdapterurus of the Kile and 

 Senegal. In the second part the lecturer discussed the anatomical 

 character and morphological significance of the electrical organ in 

 the torpedo, and in the third its mode of action, with special reference 

 to the recent investigations of Mr. Francis Gotch, Assistant in the 

 Physiological Department at Oxford. The description given of the 

 structure of the organ was also founded on new investigations by 

 Prof. Ewart, of Edinburgh, who had been good enough to prepare 

 drawings on glass, suitable for projection on the screen, of his 

 microscopical preparations. The first of these drawings showed a 

 section of the already active electrical organ of a torpedo just born. 

 It was seen to consist of a great number of tubular columns which 

 extended from the upper (dorsal) to the lower (ventral) surface of 

 the flattened body of the animal, which were as closely packed 

 together as the cells of a honeycomb, each column being divided 

 into very narrow compartments by nearly horizontal partitions of 

 extremely fine membrane. It was next pointed out that, although 

 the whole organ is made up in the common torpedo of as many as 

 500 such columns (in some species many more), each column is in 

 structure and in function an electrical organ of itself ; and not only 

 so, but that each of the fine membranous partitions or plates is au 

 electromotive structure of which, notwithstanding its almost incon- 

 ceivable tenuity, the two opposite surfaces are, when in activity, in 

 different electrical states ; so that, in consequence of their pile-like 

 arrangement and their all acting in the same direction, the electro- 

 motive force excited by the whole column is, as in a voltaic battery, 

 equal to the sum of the forces exerted by the many hundreds of 

 plates of which it is composed. 



It having thus been made evident that everything depended on 

 the plates, the lecturer proceeded to explain their minute structure, 

 for the investigation of which it was of course necessary to employ 

 much higher powers. The microscopical drawings which were 

 thrown on the screen showed that each of the fine membranes which 

 had been described consists of two different structures. Its upper 

 surface pi'esents a layer of apparently homogeneous material in which 



Ann. & Mag, N. Hist. Ser. 5. Vol xx. 31 



