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Craig shot the word out so that it had its full effect on his little audience. Then he paused, lowered his voice, and resumed on a new subject.

“Up in the Washington Heights Hospital,” he went on, “is an apparatus which records the secrets of the human heart. That is no figure of speech, but a cold scientific fact. This machine records every variation of the pulsations of the heart with such exquisite accuracy that it gives Dr. Barron, who is up there now, not merely a diagram of the throbbing organ of each of you seated here in my laboratory a mile away, but a sort of moving-picture of the emotions by which each heart here is swayed. Not only can Dr. Barron diagnose disease, but he can detect love, hate, fear, joy, anger, and remorse. 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. Yet just that slight little current is enough to sway the gossamer strand of quartz fibre up there at what we call the ‘heart station.’ So fine is this machine that the pulse-tracings produced by the sphygmograph, which I have used in other cases up to this time, are clumsy and inexact.”

Again he paused as if to let the fear of discovery sink deep into the minds of all of us.

“This current, as I have said, passes from each one of you in turn over a wire and vibrates a fine quartz fibre up there in unison with each heart here. It is one of the most delicate bits of mechanism ever made, beside which the hairspring of a watch is coarse. Each of you in turn, is being subjected to this test. More than that, the record up there shows not only the beats of the heart but the successive waves of emotion that vary the form of those beats. Every normal individual gives what we call an ‘electro-cardiogram,’ which follows a certain type. The photographic film on which this is being recorded is ruled so that at the heart station Dr. Barron can read it. There are five waves to each heart-beat, which he letters P, Q, R, S, and T, two below and three above a base line on the film. They have all been found to represent a contraction of a certain portion of the heart. Any change of the height, width, or time of any one of those lines shows that there is some defect or change in the contraction of that part of the heart. Thus Dr. Barron, who has studied this thing carefully, can tell infallibly not only disease but emotion.”

It seemed as if no one dared look at his neighbour, as if all were trying vainly to control the beating of their own hearts.

“Now,” concluded Kennedy solemnly as if to force the last secret from the wildly beating heart of some one in the room, “it is my belief that the person who had access to the operating-room of the Novella was a person whose nerves were run down, and in addition to any other treatment that person was familiar with the ether phosphore. This person knew Miss Blaisdell well, saw her there, knew she was there for the purpose of frustrating that person’s own dearest hopes. That person wrote her the note, and knowing that she would ask for paper and an envelope in order to answer it, poisoned the flap of the envelope. Phosphorus is a remedy for hysteria, vexatious emotions, want of sympathy, disappointed and concealed affections–but not in the quantities that this person lavished on that flap. Whoever it was, not life, but death, and a ghastly death, was uppermost in that person’s thoughts.”