Breathing with the Earth
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This idea was later confirmed by findings that microbes at Rio and in
New Zealand were south-seekers.
Blakemore's electron micrographs soon revealed a surprising structure.
Each bacterium contained within it, like a chain of cut jet stones, a
straight line of magnetite microcrystals. Surrounded by a thin mem-
brane, each of these particles was a single domain, the smallest piece of
the mineral that could still be a magnet.
Blakemore's bacteria led Gould to look for similar crystals in bees and
pigeons. Since an electron microscope survey of even a bee's brain would
take several lifetimes, he examined the insects with a SQUID magne-
tometer. After confirming that they were magnetic, he dissected them
and narrowed the location down to a part of the abdomen. Using the
same method, Walcott and Green dissected the heads of two dozen
pigeons, gradually subdividing them with nonmagnetic probes and scal-
pels. After a painstaking search the investigators found a tiny magnetic
deposit in a 1- by 2-millimeter piece of tissue richly festooned with
nerves, on the right side of the head, between the brain and the inner
table of the skull. The same dot of tissue contained yellow crystals of the
iron-storage protein ferritin, indicating that the pigeons, like the bacte-
ria, synthesized their own lodestone crystals.
As usual, these recent answers have raised plenty of new questions.
The existence of magnetic sensors in such diverse creatures as bacteria,
bees, and birds—the current count of species with magnetic organs is
twenty-seven, including three primates—suggests that a magnetic sense
has existed from the very beginning of life, perhaps only to be perfected
by creatures that need to get around a lot. Do all animals, then, have
the same sensors, and do they always serve the same function? How is
the information read out of the crystals by the nervous system and trans-
lated into directions? What aspect of the earth's field do these organs
sense?
Keeton noticed an especially odd thing about his pigeons' flight pat-
terns. When flying on visual flight rules by sun compass, they would
circle once, get their bearings, then move off straight toward Ithaca. But
when using their magnetic compass, the birds would fly due west from
their release point until they got out over Lake Ontario, due north of
Ithaca. Then, out of sight of land, they would make a right-angle turn
to the left and follow the exact meridian of home. Keeton told me this
but never published the observation because he didn't know what to
make of it. He said, "I asked a physicist: 'Are they making contact with
a certain magnetic
line of force?' The man said, 'No, magnetic lines of
force an just an arbitrary convention we use to symbolize a field and