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The employment of the Galvanometer instrument for accu-
racy and delicate purposes also requires the utmost precaution.
It is necessary, first of all, to avoid any chemical action, even of
the animal liquids, upon the platinum plates, which serve to
bring into the circuit the various organs or tissues whose electric
Fig. 14. Galvanometer.
state we are studying. To this end we must use pure platinum
plates of equal size, cleansed with exact care. Then we must
even allow them to be plunged into pure water for some time, to
prevent the simple immersion from giving rise to some current,
as it is so liable to do. When thus quite sure there is no action,
we then touch at the same time, with these two poles insulated,
the animal parts to be tested. But the mere fact of the circula-
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