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This machine is known as the Einthoven 'string
galvanometer,' invented by that famous Dutch physiologist of
Leyden."
There was a perceptible movement in our little audience at the
thought that the little wires that ran back of the screen from the
arms of each were connected with this uncanny instrument so far
away.
"It is all done by the electric current that the heart itself
generates," pursued Kennedy, hammering home the new and startling
idea. "That current is one of the feeblest known to science, for
the dynamo that generates it is no ponderous thing of copper wire
and steel castings. It is just the heart itself. The heart sends
over the wire its own telltale record to the machine which
registers it. The thing takes us all the way back to Galvani, who
was the first to observe and study animal electricity. The heart
makes only one three-thousandth of a volt of electricity at each
beat. It would take over two hundred thousand men to light one of
these incandescent lamps, two million or more to run a trolley-
car.


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