Personal Narrative Of Travels To The Equinoctial Regions Of America During The Years 1799-1804 - Volume 2 - By Alexander Von Humboldt And Aime Bonpland.
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M. Provencal And Myself Have Proved By Our Researches On
The Respiration Of Fishes, That Their Humid Bronchiae Perform The
Double Function Of Decomposing The Atmospheric Air, And Of
Appropriating The Oxygen Contained In Water.
They do not suspend their
respiration in the air; but they absorb the oxygen like a reptile
furnished with lungs.
It is known that carp may be fattened by being
fed, out of the water, if their gills are wet from time to time with
humid moss, to prevent them from becoming dry. Fish separate their
gill-covers wider in oxygen gas than in water. Their temperature
however, does not rise; and they live the same length of time in pure
vital air, and in a mixture of ninety parts nitrogen and ten oxygen.
We found that tench placed under inverted jars filled with air, absorb
half a cubic centimetre of oxygen in an hour. This action takes place
in the gills only; for fishes on which a collar of cork has been
fastened, and leaving their head out of the jar filled with air, do
not act upon the oxygen by the rest of their body.
The swimming-bladder of the gymnotus is two feet five inches long in a
fish of three feet ten inches.* (* Cuvier has shown that in the
Gymnotus electricus there exists, besides the large swimming-bladder,
another situated before it, and much smaller. It looks like the
bifurcated swimming-bladder in the Gymnotus aequilabiatus.) It is
separated by a mass of fat from the external skin; and rests upon the
electric organs, which occupy more than two-thirds of the animal's
body. The same vessels which penetrate between the plates or leaves of
these organs, and which cover them with blood when they are cut
transversely, also send out numerous branches to the exterior surface
of the air-bladder. I found in a hundred parts of the air of the
swimming-bladder four of oxygen and ninety-six of nitrogen. The
medullary substance of the brain displays but a feeble analogy with
the albuminous and gelatinous matter of the electric organs. But these
two substances have in common the great quantity of arterial blood
which they receive, and which is deoxidated in them. We may again
remark, on this occasion, that an extreme activity in the functions of
the brain causes the blood to flow more abundantly towards the head,
as the energy of the movement of the muscles accelerates the
deoxidation of the arterial blood. What a contrast between the
multitude and the diameter of the blood-vessels of the gymnotus, and
the small space occupied by its muscular system! This contrast reminds
the observer, that three functions of animal life, which appear in
other respects sufficiently distinct - the functions of the brain,
those of the electrical organ, and those of the muscles, all require
the afflux and concourse of arterial or oxygenated blood.
It would be temerity to expose ourselves to the first shocks of a very
large and strongly irritated gymnotus. If by chance a stroke be
received before the fish is wounded or wearied by long pursuit, the
pain and numbness are so violent that it is impossible to describe the
nature of the feeling they excite. I do not remember having ever
received from the discharge of a large Leyden jar, a more dreadful
shock than that which I experienced by imprudently placing both my
feet on a gymnotus just taken out of the water. I was affected during
the rest of the day with a violent pain in the knees, and in almost
every joint. To be aware of the difference that exists between the
sensation produced by the Voltaic battery and an electric fish, the
latter should be touched when they are in a state of extreme weakness.
The gymnoti and the torpedos then cause a twitching of the muscles,
which is propagated from the part that rests on the electric organs,
as far as the elbow. We seem to feel, at every stroke, an internal
vibration, which lasts two or three seconds, and is followed by a
painful numbness. Accordingly, the Tamanac Indians call the gymnotus,
in their expressive language, arimna, which means something that
deprives of motion.
The sensation caused by the feeble shocks of an electric eel appeared
to me analogous to that painful twitching with which I have been
seized at each contact of two heterogeneous metals applied to wounds
which I had made on my back by means of cantharides. This difference
of sensation between the effects of electric fishes and those of a
Voltaic battery or a Leyden jar feebly charged has struck every
observer; there is, however, nothing in this contrary to the
supposition of the identity of electricity and the galvanic action of
fishes. The electricity may be the same; but its effects will be
variously modified by the disposition of the electrical apparatus, by
the intensity of the fluid, by the rapidity of the current, and by the
particular mode of action.
In Dutch Guiana, at Demerara for instance, electric eels were formerly
employed to cure paralytic affections. At a time when the physicians
of Europe had great confidence in the effects of electricity, a
surgeon of Essequibo, named Van der Lott, published in Holland a
treatise on the medical properties of the gymnotus. These electric
remedies are practised among the savages of America, as they were
among the Greeks. We are told by Scribonius Largus, Galen, and
Dioscorides, that torpedos cure the headache and the gout. I did not
hear of this mode of treatment in the Spanish colonies which I
visited; and I can assert that, after having made experiments during
four hours successively with gymnoti, M. Bonpland and myself felt,
till the next day, a debility in the muscles, a pain in the joints,
and a general uneasiness, the effect of a strong irritation of the
nervous system.
The gymnotus is neither a charged conductor, nor a battery, nor an
electromotive apparatus, the shock of which is received every time
they are touched with one hand, or when both hands are applied to form
a conducting circle between the opposite poles.
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