Donatella Lippi
Giuseppe Mascia
Luigi Padeletti
Florence, Italy

Doctors since time immemorial have felt the pulse of their patients, noting its regularity, frequency, strength, and breadth, at times using colorful expressions to variously describe it as “formicant” or “vermicular” (ant-like or worm-like),¹ and diagnosing “love sickness” in maidens by the presence of the so-called pulsus amatorius. (Fig 1.) They were not able, however, to count the beats, and clocks used at that time were not useful for that purpose.²

Following Galileo’s discovery of the isochronism of the pendulum in 1602, seventeenth century scientists quickly perceived its applications, introducing quantitative methods into medicine and inventing medical devices to measure physiological phenomena in the human body. Among these scientists was Sanctorius Sanctorius (1561–1636), professor of theoretical medicine at the University of Padua,³ who performed experiments in temperature, respiration, and weight.

Sanctorius studied digestion by constructing a wooden frame that supported a chair, a bed, and a work table. Suspended from the ceiling with scales, the frame recorded changes in weight. For thirty years he weighed himself together with everything he ate and drank, as well as his urine and faeces, and recorded how much his weight changed after eating, fasting, and excreting.⁴ His theory of “perspiratio insensibilis” was an attempt to account for differences in body weight, as he believed that weight was gained or lost through the pores or during respiration.⁵

But Sanctorius’ reputation rests on his invention of a device for measuring the pulse, which he called the pulsilogium. (Fig 2.) In his work entitled Methods to avoid errors occurring in medical art, he wrote: “In order to commemorate quickly and exactly my knowledge on the pulse of a patient, I have invented the pulsemeter (pulsilogium), which makes it possible to measure exactly the beats of the arteries . . . and to compare them with the beats of earlier days. . . .With the help of the pulsemeter, we can monitor at what day and at which hour the pulse deviated in intensity and frequency from its natural state.”⁶

Sanctorius used the physics of the pendulum to determine the pulse rate, according to Galileo’s observation that the frequency of the pendulum swing was inversely proportional to the square root of its length. The tool was a leaden bullet at the end of a linear or silk cord, and the oscillation on the pendulum was adjusted by changing the length of the cord to match or synchronize with the pulse beat.⁷ The pulse rate corresponded to the position of a knot in the cord on a horizontal ruler, or to the location of the hand on the dial. This instrument had the cord wound around a drum, and as the drum rotated to change the cord length, the hand moved around the dial.⁷ Thanks to the pulsilogium, Sanctorius gave the first description of the circadian rhythm of the cardiac frequency. He considered a pulse rate of seventy as normal.

Pivotal in the use of the pulsilogium was the physician, who had to adjust the length of the pendulum until a periodic synchrony was achieved between oscillation and pulse. The pulse rate was referred to in units of length. The pulsilogium was used by the Dutch physician and schoolmaster Isaac Beeckman (1588–1637), a great representative of the mechanical philosophy and an expert technician. He had become interested in pendulum motion in 1618, making similar observations to Galileo’s, inventing many applications for a continuously regular pendulum, such as a metronome (a pendulum with a swing of exactly one second, to be used as a universal measure of length), a pulsilogium for counting the human pulse, and a pendulum clock to determine the longitude at sea. Some years later, the clock-maker Samuel Watson (fl. c. 1687–1710) constructed for Sir John Floyer (1649–1734) the first known stop watch, and also the first watch with a second hand. Floyer was sure that the pulse would reveal otherwise imperceptible information about the movement of the blood and other bodily fluids and he spent most of his life creating charts and tables relating the pulse rate to diseases, sex, age, respiration rate, body temperature, and much more.⁸ The sixty-second minute thus became the standard for pulse measurement.⁹ Therefore, Sir John Floyer is credited to be the first physician to time the pulse accurately.

It cannot be said that the new device became widely used. But in the Netherlands, Isaac Beeckman stimulated a lively interest in it, this at a time when lovesick maidens were regarded as being “feverish, with an erratic pulse”¹⁰ and the diagnosis of love sickness was based on evaluating the so-called pulsus amatorius. This undoubtedly pricked the interest of Jan Steen (1626–1679), as shown by several of his paintings featuring a doctor in a serious mood visiting a lovesick maiden and taking her pulse.¹¹ But in Steen’s native town of Leiden, home of a famous medical school, doctors were frequent targets of parody. As shown in Steen’s paintings, the doctor’s clothing is outdated, looking more like a theatrical costume. The artist’s intent clearly was to mock old fashioned physicians, who presumably would have had no interest in using a new-fangled device that could even upset the doctor-patient relationship. Moreover, to be useful, it would have needed a skilled, open-minded professional; and an old-fashioned doctor would not have welcomed this novelty with open arms. This is Jan Steen’s punchline.

References

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