4.20 Note 29: electrical fishes 



is really from head to tail through the organ, so that the tail becomes positive 

 with respect to the head, and Schultze, who had been led to believe, from a 

 comparison of his own observations on the organs of pseudo-electric fishes with 

 the drawings of Bilharz, that the nerves might pass through the diaphragms 

 and terminate on their anterior surfaces, found, on examining the preparations 

 sent him by Du Bois Reymond, that this was really the case in Malapterurus, 

 so that we may now assert that in every known case the terminations of the 

 nerves are on that side of each diaphragm which during discharge becomes 

 negative. 



The origin of the nerves which supply the electric organs is different in the 

 three families. 



In the Torpedos the electric nerves are derived from the posterior division 

 of the brain. Irritation of this lobe produces an electric discharge of the organ, 

 but no muscular contraction. Irritation of other parts of the brain produces 

 muscular contractions, but not electric discharges, unless the disturbance pro- 

 duced affects the electric nerves. 



In the Gymnotus the electric nerves arise from the whole length of the 

 spinal cord, and in Malapterurus the electric organs are supplied by the 2 n<1 

 and 3 rd pair of spinal nerves. 



The electric nerves are so called because they govern the discharges of the 

 electric organ. No essential difference has been observed between the electric 

 phenomena in these nerves and those in other nerves. They must be classed, 

 with respect to origin as well as function, among the motor nerves. The only 

 difference is that their function is to govern the electric discharge of a peculiar 

 organ, instead of the contraction of a muscle. 



The experiments of Dr Davy* and those of Matteuccif showed that the 

 discharge of the Torpedo produces all the known phenomena of an electric 

 discharge. Faraday J did the same for the Gymnotus, and Du Bois Reymond 

 for the Malapterurus. 



M. Marey[| has recently investigated some of the electrical phenomena of 

 the discharge of the Torpedo. He employed three methods of indicating the 

 discharge, the prepared leg of a frog, which is extremely sensitive to the feeblest 

 current, but has the disadvantage that the time required for the contraction 

 of the muscles, and still more the time required for their relaxation, is many 

 times the period of the recurrence of the electric discharges of the Torpedo, so 

 that the rapidly changing phases of the discharge cannot be distinguished by 

 this method. 



The second indicator used by Marey was the electromagnetic signal of 

 M. Deprez, which can register 500 electric currents in a second by the motion 

 of a tracing point over the smoked surface of a revolving cylinder. The action 



* Phil. Trans. 1834. f Comptes Rendus, 1836. 



J London Medical Gazette, 1838. Berlin Monatsb. 1858. 



II Travaux du Laboratoire de M. Marey, in. (1877). 



