336 ELECTRO-PHYSIOLOGY. 



same direction being always observed — that is, from the point neai-est the back 

 to the point nearest the belly in the ai'C of the galvanometer. In a word, the 

 poles or polar surfaces are the dorsal and the ventral surface of the organ. 



In operating with the galvanometer on the gymnotus, a strong deviation is 

 likewise obtained in the act of the discharge, by placing the extremities of the 

 instrument in contact with those of the animal. All other circumstances being 

 equal, the deviation increases by increasing the surface of the electrodes in con- 

 tact with the fish, and this is distinctly seen in the torpedo. In proportion as 

 the extremities of the galvanometer approach one another towards the middle of 

 the gymnotus the discharge is diminished, and the same occurs when the dis- 

 charge is received with the hands. With the gymnotus the discharge is directed 

 in the galvanometer from the head to the tail of the fish. 



Quite recently Ranzi, an eminent surgeon, whose loss Italy still deplores, re- 

 ceived from me, on the occasion of a visit which he made to Egypt, instruments 

 and instructions for stud3dng the discharge of the silurus of the Nile, and to 

 him we owe the discovery of the direction of the discharge in that fish, a dis- 

 covery since verified at Berlin in a living silurus. In this fish, whose body is 

 also elongated, the poles of the electrical organ are at the extremities of its body, 

 but, strangely enough, in opposition to the gymnotus, the positive pole is hero- 

 towards tlic tail and the negative pole towards the head. 



After having thus shown the electrical phenomena of the discharge of the 

 torpedo, phenomena which cannot differ from those of other electrical fishes, we 

 should now proceed to state the principal facts on which the theory of these 

 animal electro-motors is founded. But it is necessary first to give some account 

 of the structure of the electric organs, which does not essentially differ in one 

 fish and another. In general the organ in question is constituted by an albumin- 

 ous liquid contained in certain cylindrical or prismatic cavities which have a 

 membi-anaceous envelope and are separated transversely by partitions of very 

 thin membrane. These masses or prismatic columns arc disposed in the tor- 

 pedo with their bases in contact with the skin of the back and belly, and hence 

 when the fish is in its natural position the prisms are vertical. In the gymnotus, 

 on the contrary, the prisms are horizontal and parallel to the axis of the body, 

 and have their bases at the head and at the tail of the animal. Analogous to 

 the structure of the organ of the gymnotus is that of the organ of the siUirus. 



The chemical composition of the substance of the organ is that of the liquid 

 which fills the prisms and the cellules of which these are composed, and which 

 is in great jiart a solution of albumina; a thousand parts of the substance of the 

 organ of the torpedo contain 903.4 of water. The fresh substance of the organ 

 is neutral, and it is only on leaving it for some time in the air that its consistency 

 is found to diminish, when it becomes partially fiuid, and then offers a slight 

 alkaline reaction. A part of the composition of the organ is formed by the cel- 

 lular matter and a considerable quantity of fatty matter containing phosphorus, 

 Avhich is probably due to the great number of nervous filaments distributed in 

 the electric organ. Anatomists have found that the nerves of this organ have 

 in different fishes a different origin. In the torpedo these nerves proceed from 

 the fifth and eighth pair, while in the gymnotus the nerves of the organ are all 

 spinal nerves. The brain of the torpedo is distinguished by a large mass which 

 stretches behind the olfactory and optic lobes and the cerebellum, a mass which 

 exists only in a rudimentary state in the brain of fishes of the same species. 

 This mass, which is called the fourth or electric lobe, seems to consist of an ex- 

 pansion of the medulla elongata, and is composed in part of elementary fibres 

 which furnish nerves to the organ, and especially of gray and ganglionic matter. 



Hunter counted in an organ of the torpedo four hundred and seventy prisms, 

 and succeeding anatomists have ascertained that each of these prisms contains 

 about two thousand superposed cellules. The prisms of the gymnotus are con- 

 siderably longer than those of the torpedo, for they extend almost from one ex- 



