576 THE PHYSIOLOGY OF ELECTRICAL ORGANS. 



and allows any electrical effect in the organ to traverse the galvano- 

 meter ; that of the third (K 3 ) breaks the galvanometer circuit, and hence 

 the instrument is only influenced by electromotive changes occurring 

 between the opening of K 2 and of K 3 . By suitable arrangements, the 

 time between K x and K 2 may be varied, whilst that between K 2 

 and K 3 remains always of some fixed short duration, such as '001 sec. 

 or less. 



By moving K 2 and K 3 towards or away from K x before each passage 

 of the traveller, and noting the galvanometric deflections produced by 

 such a passage with its consequent excitation, data are obtained from 

 which the total development of the response may be inferred. The 

 repeating rheotome has also been used in the Naples laboratory, by 

 Schonlein, for the same purpose. 



The first and most obvious fact is the existence of a period of delay 

 between the excitation and the commencement of the response. Every 

 preparation shows such a period of delay, the so-called latent period. 

 If the preparation is excited by the stimulation of its nerve, then the 

 delay is in the case of Torpedo perceptibly increased, in proportion as 

 the seat of the stimulus is removed from the nerve termination in the 

 organ. The increase has been shown to be accounted for by the 

 propagation rate along the nerve of the excitatory state thus aroused, 

 which, in the case of the electrical nerves of Torpedo, may be as little as 

 9 metres per second at 5 C., although at 20 C. it is 30 metres per second. 

 At 15 C. a rate of from 15 to 20 metres per second has been observed. 1 



In Malapterurus preparations, on the other hand, change in the 

 delay, due to the seat of the nerve excitation, is far less marked, and 

 the propagation rate in the electrical nerve of this organ is, at 12 C., 

 at least as fast as that in the motor nerve, i.e. 40 metres per second. But 

 even when the nerve is excited close to the organ, a distinct delay 

 occurs, and a fact of great significance is the remarkable circumstance 

 that, when the exciting current is allowed to traverse the organ itself, 

 the duration of the period of delay is not perceptibly different. 2 It 

 will be remembered that in frog's muscle a very appreciable diminution, 

 amounting to 0'003 second, at a temperature of 15 C., occurs in the 

 delay to direct, as compared with that to indirect, excitation. 



The absence of any such diminution in the case of the electrical organ 

 is in favour of the view that the organ response is that of a structure 

 which cannot be separated from the nerve-endings. These are excited 

 whether the stimulus is applied to the entering trunk of the nerve, or 

 to the nerve fibres contained in the discs. It follows from this that the 

 organ owes its susceptibility to excitation entirely to the nerves which 

 it contains, and that, apart from these, its substance is inexci table. A 

 further inference may be hazarded. If the plates, apart from the nerve- 

 endings, are inexcitable, then the seat of the excitatory change, that is 

 the electrical response, being localised in the nerve-endings of the 

 plate, the function of the protoplasmic substance remains at present 

 unknown. An additional confirmation of the view that the discs apart 

 from the nerves are inexcitable, is furnished by the observations of 

 Garten on the result of nerve section. Torpedoes, the electrical nerves 

 of which had been previously divided on one side, showed, nineteen days 

 after section, complete inexcitability of the organ of this side to both 



1 Schonlein, loc. cit.; Gotch, Phil. Trans., London, 1887, vol. clxxviii. B. 



2 Gotch and Burch, loc. cit. 



