5 68 THE PHYSIOLOGY OF ELECTRICAL ORGANS. 



innervated by the branches of one axis cylinder, and each compart- 

 mental branch itself divides, forming line terminations in the proto- 

 plasmic lining of the compartmental wall, it will be evident that the 

 Malapterurus organ affords an instance of the peripheral distribution of 

 a single nerve cell process upon a far more extensive scale than can be 

 traced in any other known structure. It has been estimated that the 

 chief compartmental branches entering the organ have a cross-sectional 

 area 350,000 times that of the axis cylinder process of the nerve cell. 



The foregoing brief description of the structural features of electrical 

 organs is by no means an exhaustive one. It is merely intended to 

 portray the most striking of such features, and the reader is referred 

 to the excellent account given by Biedermann in his " Electro-physiology " 

 for other details. 1 The space allotted to the subject admits of but a 

 restricted reference to the chief points in connection with it, and the 

 same is true in regard to the functional activity of the organ. This can 

 only be dealt with in the present article so as to touch upon its most 

 prominent characteristics, but attention will be drawn to such recent 

 discoveries as appear to have a general interest in connection with nerve 

 muscle phenomena. 



THE FUNCTIONAL ACTIVITY OF THE ORGAN. 



The peculiar features of the structure of an electrical organ, as 

 described in the preceding paragraphs, are the existence of distinct 

 protoplasmic expansions or discs, their situation in separate com- 

 partments arranged in series one behind the other, and the presence on 

 each disc of an innervated surface. Such an arrangement is eminently 

 adapted for the functional purposes of an electric organ. For if 

 the functional activity of any one disc is dependent upon the nerve- 

 endings it contains, and displays itself by electromotive changes such 

 that electrical currents traverse the disc from one surface to the 

 other, then, since the liquid contents of the compartment furnish 

 a conducting medium of low resistance for such currents, these must 

 traverse the whole series of superimposed discs. When, therefore, 

 similar electromotive changes are simultaneously established in all 

 the plates of a column, the resultant effects must be summed, and a 

 large total electromotive change is thus produced. The principle upon 

 which each organ is constructed resembles in this respect that of the 

 voltaic pile with columns of superimposed pairs of elements arranged 

 in series ; in such a pile the ends of the columns will be the points of 

 maximal potential difference which, with an extensive pile of discs, may 

 be very considerable. 



As regards the direction of the electrical currents, which are present 

 during functional activity, the simplest experiments show that this is 

 definite and unvarying for any organ, and that the line of flow is through 

 the discs from one surface to the other. Pacini first drew attention to a 

 supposed relationship between such direction and the minute structure 

 of the protoplasmic disc. In the organs then accurately known, the 

 surface of the disc which receives the entering nerves is so altered 

 during the excitatory state, that it becomes galvanometrically negative 

 to the opposite one, and thus the currents, which during activity traverse 



1 Biedermann, "Electro-Physiology," translated by F. A. Welby, London, 1898, vol. ii. 

 p. 357-407. 



