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 'electrocardiogram,' which follows a certain type. The photographic film on which this is being recorded is ruled so that at the heart station Dr. Barren 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.
