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Physiological

electric, electrical, organs, fishes and currents

PHYSIOLOGICAL.

Perhaps the best-known of all the investigators of electric fishes is DuBois-Reymond. The founder of electro-physiology, he has ex haustively covered the subject of electrical currents in muscle, nerves, and electrical organs, carrying on, in the early eighties, a prolonged dispute with Hering (w) and Hermann (58. 59) concerning the extent of polarization arising in a muscle when an electrical current has been passed through it. DuBois-Reymond experimented on living Malop terurus and on living Torpedo in Berlin, and under his direction Sachs worked on living Gymnotus in South America. Their combined results are so comprehensive and so accurate as to leave room for no further investigation of the same nature, and the name of DuBois-Reymond is recognized to be that of the leader in the physiological researches on animal electricity.

Cavendish in 1780 (26) was the first to conceive of the idea of current curves and to imitate the shock of Torpedo by ordinary electricity. He was far in advance of his time and it was not until a century later that Faraday (a) reached the same opinion. Although it has since been possible by modern methods and apparatus to considerably modify and correct the current-curves of Cavendish, the basic idea remains his.

In 1831 Colladon of Geneva, experimenting on the Torpedo, gave the name of "Collation's currents" to those currents running between points on either the ventral or the dorsal surface OW . A few observa tions were made the same year by Matteuci (72), but not until the discovery by Bilharz in 1857 (16) was any further advance made in the study of the electrical currents. DuBois-Reymond then calculated that "the greater the length of a Torpedo column, provided the number of plates in the unit of length is the same, so much greater must be its electromotive force; and by as much as the columns diminish in height from the inner to the outer edge of the organ, by so much may the electromotive force of the median columns be greater than that of the outer ones" (is). At the same time he discussed the matter of immu nity in electric fishes, finding that all electric fishes are practically immune to their own shock and relatively so to the shock of another fish of the same species, much as a viper is immune to its own poison, in spite of the fact that the body of the fish is much more favorably placed to receive the shock than are the bodies of neighboring fishes. Definite electric currents are known to pass through the body of the fish. They have been detected in the digestive tract, in the brain and spinal cord, and found to be of appreciable intensity, yet the fish remains apparently unaware of the shock.

Marey in 1879 (71) was the first to represent graphically the reflex currents of Gymnotus and Torpedo by the use of the telephone. Schon lein (a) repeated the experiments with a galvanometer and calculated the voltage of the individual electroplaxes in Torpedo and in Raja; Cremer (Gotch so) used the "saitenelektrometer" of his own invention, and in 1899 Garten (es) made very accurate measurements and records with the capillary electrometer. In 1881 Sachs (so) published his work

on the physiology of the organs of Gymnotus; while Gotch and Burch (52. as) and Koike (es) have independently published similar works on Malopte-rurus, so that the shock in these three fishes has been ex haustively investigated. The general results have shown that electric organs have much the same electrical properties as muscles and nerves, with the difference that in the case of the electric organs the elements are considerably modified and so arranged in series as to give the effect of a battery in which an otherwise insignificant current can be made measurable by addition (Gotch so).

Gotch and Burdon-Sanderson (27, 22) followed up these experiments on the weak electric fishes, finding them to be similar in both the Rajithe and the Monnyridie to those of the strong electric fishes, except in the intensity of the shock. The true electrical nature of these organs, which had been previously considered electrical from their structure but had not been determined by experiment as to function, was now ascertained, for definite electrical currents could be detected by the galvanometer.

The combined results of these investigators, notwithstanding certain prolonged controversies, have led to a pretty definite agreement as to the nature of the activity of these organs. The activity of the electric organs is dependent upon the arrangement of the electrical plates in a linear series for its adequate expression, and the columnar structure of the organ thus modifies rather than determines the characteristics of the activity. The nature of these activities lies in the electrical change in the nerves themselves, expressed through the agency of the electroplaxes. That the disk is the excitable structure responding to impulses from the nerves is an abandoned theory contradicted by all experimental evidence, for such paralyzing drugs as atropin and curare, which are known to effectively destroy the action of muscle tissue, have no effect upon the activity of the electric organs unless given in such doses as to paralyze the nerves themselves. All the effects in the electrical organs are connected with excitation, and its concomitant alteration, which is always accompanied in the nerve by rapid electric changes, while the structural nature of the organ is such that the changes in each group of nerve terminations may become con spicuous by summing with those of the neighboring groups (Gotch u).

Another law which has been generally accepted is that of Pacini, in connection with the probable direction of the current in the different electric fishes. He states that the electric current will run from the electric layer where the nerve-endings are, to the nutritive layer, so that the electric surface will be negative to the nutritive one. Experi ment has so far verified this law in every case which has been examined in this regard, except in that of Malopterurus, in which the current goes in the opposite direction, namely, from the nutritive to the electric layer.