Thread by @thomasngmorris

This historic document is the first electrocardiogram (ECG), recorded in 1887 by the British physiologist Augustus Desiré Waller.

By the 1880s, experiments had already shown that electrical activity played an important role in cardiac function. In 1878 John Burdon-Sanderson demonstrated the sequence of tissue depolarization and repolarization that accompanied the beating of a frog's heart.

In 1885, Waller (r) started to investigate electrical activity in animal hearts using a Lippmann capillary electrometer, an instrument which employed a column of mercury to detect electrical current. Tiny deflections in the height of the column were observed through a microscope.

One day in 1887, as Waller later explained, "it occurred to me that it ought to be possible to use the limbs as electrodes and thus lead off from the heart to the electrometer without exposing the heart".

Waller continues: "I dipped my right hand and left foot into a couple of basins of salt solution, which were connected with the two poles of the electrometer and at once had the pleasure of seeing the mercury column pulsate with the pulsation of the heart."

To record this phenomenon for publication he shone a light through the tube containing the mercury column, and mounted a photographic plate on a toy train - an ingenious way of turning the pulsations of the mercury into a linear trace.

He first used this recording method in May 1887. This time the electrodes were attached to the front and back of the subject's chest. NB the ECG is the lowest of the three traces on this graph: the top line records time, the middle is the pulse wave recorded by a sphygmometer.

The paper in which this appeared is a landmark in cardiac electrophysiology. Yet Waller himself was under the impression that the ECG would be useful to experimental physiologists rather than a helpful diagnostic aid.

An aside: this is Waller with his beloved bulldog Jimmy, who was his assistant in many a physiological demonstration.

Jimmy often appeared at Waller's demonstrations, obediently putting his paws in saltwater electrodes so that Waller could demonstrate the electrical activity of his heard.

Jimmy was even the subject of a Parliamentary question. In 1909 the Home Secretary Herbert Gladstone (son of William Ewart, the former prime minister) defended the dog's public appearances, explaining that they were painless and Jimmy enjoyed them.

Waller's was the first ECG to be recorded and published. But it was the Dutch physician Willem Einthoven who turned the invention into a clinical tool - in 1895 he developed his electrocardiogram, an invention which subsequently won him a Nobel Prize.