Picture - Cosmic Polymath

ANIMAL MAGNETISM 123
the electric organs and the spinal cord and brain sufficiently account for the control the fish has over them, and the
rich blood supply accounts for their high organisation and great activity. They are as completely under control as
ordinary voluntary muscles, and many are of opinion that the electric and muscular systems have many points
in common.
The resemblance is traced in several directions : {a) in development ; from researches into the development
of the electric organ of Torpedo it is supposed that the organ in question is developed from muscular substance ;
(b) peculiar muscular organs, the functions of which have not been discovered, are found in the rays, Mormyrus
and Gymnarchus ; (c) the electric organ and muscle behave similarly under the same circumstances. Thus, if the
electric organ and muscle be exhausted, from whatever cause, they require rest and nourishment to restore them
to their normal state. If strychnia be administered, a rapid succession of involuntary electric discharges is induced
in the one, and tetanic convulsions in the other. If the motor nerves distributed to the electric organ and muscle
under such circumstances, artificial activity may
be divided, the brain loses its initiating and controlUng power :
be induced by irritating the peripheral cut ends of the nerves going to the electric organ and muscle respectively.
The more healthy and vigorous the electric organ and muscle and their possessors, the more severe the shock given,
and the greater the muscular force evolved.
" All muscles evolve a constant stream of electricity, which may be shown by a multiplying galvanometer to
pass from the long external surface, which is positive, to the transversely cut section, which is negative. . . . Du
Bois-Reymond discovered that, hke muscles, nerves possess an electric current, but much weaker, running from the
longitudinal external surface, which is positive, to the transverse internal one, which is negative." ^
The brain, as indicated, exercises supreme control over the electric organ and muscle alike.
The structure of the electric organ varies somewhat in the several electric fishes.
The electric fishes possessing fully formed electric organs, and which can gradually make, store, and give electric
shocks of greater or less intensity at will, are the electric rays [Torfedinidm), the electric cat or sheath-fish of tropical
Africa (Malapterurus), and the electric eel of tropical America (Gymtiotus).
The electric rays have been carefully described by Dr. Giinther as follows : " The electric organs with which
these fishes are armed are large, flat, uniform bodies, lying one on each side of the head, bounded behind by the
scapular arch, and laterally by the anterior cresoentic tips of the pectoral fins. They consist of an assemblage
of vertical hexagonal prisms, whose ends are in contact with the integuments above and below ; and each prism
is subdivided by dehcate transverse septa, forming cells, filled with a clear, trembhng, jelly-like fluid, and fined
within by an epithelium of nucleated corpuscles. Between this epithehum and the transverse septa and walls of
the prism there is a layer of tissue on which the terminations of the nerves and vessels ramify. Hunter counted
470 prisms in each battery of Torpedo marmorata, and demonstrated the enormous supply of nervous matter which
they receive. Each organ receives one branch of the trigeminal nerve and four branches of the vagus—the
former, and the three anterior branches of the latter, being each as thick as the spinal cord (electric lobes). The
fish gives the electric shock voluntarily, when it is excited to do so in self-defence or intends to stun or to kill its
prey ; but to receive the shock the object must complete the galvanic circuit by communicating with the fish at
two distinct points, either directly or through the medium of some conducting body. If an insulated frog's leg touches
the fish by the end of the nerve only, no muscular contractions ensue on the discharge of the battery, but a second
point of contact immediately produces them. It is said that a painful sensation may be produced by a discharge
conveyed through the medium of a stream of water. The electric currents created in these fishes exercise all the
other known powers of electricity ; they render the needle magnetic, decompose chemical compounds, and emit
the spark. The dorsal surface of the electric organ is positive, the ventral surface negative.
" Of the genus Torpedo six species are known, distributed over the Atlantic and Indian Oceans ;
three of them
are rather common in the Mediterranean, and one (T. hehetans) reaches the south coast of England. They attain to
a width of from two to three feet, and specimens of that size are able to disable by a single discharge a full-grown
man, and, therefore, may prove dangerous to persons bathing. Other genera, differing from the Torpedo in the
position and structure of some of the fins, are found in other tropical and sub-tropical seas, namely, Narcine, Hypnos,
Discopyge (Peru), Astrape, and Temera. All, hke electric fishes generally, have a naked body.
" A large fish, of the general appearance of a torpedo, has been found at Monte Bolca ; and Cydohatis, from the
upper cretaceous hmestone of Lebanon, is probably another extinct representative of this family."
What is said of the electric rays is, for the most part, true of the electric cat or sheath-fishes, and the
electric eels.
The electric sheath-fishes occur not unfrequently in the fresh waters of tropical Africa, and of these three
1 "Physiology, General, Special, and Pi-actical," Ijy John Hughes Bennett, M.D., F.R.H.E., &e., Professor of the Institutes of Medicine,
University of Edinburgh.