Personal Narrative Of Travels To The Equinoctial Regions Of America During The Years 1799-1804 - Volume 1 - By Alexander Von Humboldt And Aime Bonpland.
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We Observed During The Night, That,
Of Three Species Of Medusas Which We Collected, None Yielded Any
Light But At The Moment Of A Very Slight Shock.
This property does
not belong exclusively to the Medusa noctiluca, which Forskael has
described in his Fauna Aegyptiaca, and which Gmelin has applied to
the Medusa pelagica of Loefling, notwithstanding its red tentacula,
and the brownish tuberosities of its body.
If we place a very
irritable medusa on a pewter plate, and strike against the plate
with any sort of metal, the slight vibrations of the plate are
sufficient to make this animal emit light. Sometimes, in
galvanising the medusa, the phosphorescence appears at the moment
that the chain closes, though the exciters are not in immediate
contact with the organs of the animal. The fingers with which we
touch it remain luminous for two or three minutes, as is observed
in breaking the shell of the pholades. If we rub wood with the body
of a medusa, and the part rubbed ceases shining, the
phosphorescence returns if we pass a dry hand over the wood. When
the light is extinguished a second time, it can no longer be
reproduced, though the place rubbed be still humid and viscous. In
what manner ought we to consider the effect of the friction, or
that of the shock? This is a question of difficult solution. Is it
a slight augmentation of temperature which favours the
phosphorescence? or does the light return, because the surface is
renewed, by putting the animal parts proper to disengage the
phosphoric hydrogen in contact with the oxygen of the atmospheric
air?
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