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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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.
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