Lombroso’s Plethysmograph: The First Lie Detector (1895)

The Father of Criminal Anthropology

Cesare Lombroso (1835–1909) was an Italian physician, psychiatrist, and criminologist who fundamentally reshaped how the Western world thought about crime [1]Verified History of Polygraph — Ohio Polygraph Services
Confirms Lombroso was first to use hydrosphygmograph for lie detection in 1895 and that Mosso used plethysmograph from 1878. Born Ezechia Marco Lombroso on 6 November 1835 in Verona to a wealthy Jewish family [2]Verified Cesare Lombroso — Wikipedia
Confirms Lombroso born 6 November 1835 in Verona to a wealthy Jewish family, and his career timeline at the University of Turin, he studied literature, linguistics, and archaeology at the universities of Padua, Vienna, and Paris before earning his medical degree from the University of Pavia in 1858 [3]Verified Cesare Lombroso — Encyclopedia.com (Multiple entries)
Confirms Lombroso's birth, education at Pavia/Vienna/Paris, medical degree 1858, surgery degree 1859, and positions at University of Turin. He later received a degree in surgery from the University of Genoa in 1859 and served as an army surgeon during the Austro-Italian war [3]Verified Cesare Lombroso — Encyclopedia.com (Multiple entries)
Confirms Lombroso's birth, education at Pavia/Vienna/Paris, medical degree 1858, surgery degree 1859, and positions at University of Turin.

After taking charge of the mental asylum at Pesaro in 1871, Lombroso's interest in the relationship between insanity and crime deepened [4]Verified Cesare Lombroso — EBSCO Research Starters
Confirms Lombroso founded the Italian School of Positivist Criminology and his birth details and education. In 1876, he became professor of legal medicine and public hygiene at the University of Turin, the institution that would become the centre of his life's work [3]Verified Cesare Lombroso — Encyclopedia.com (Multiple entries)
Confirms Lombroso's birth, education at Pavia/Vienna/Paris, medical degree 1858, surgery degree 1859, and positions at University of Turin. He was later appointed professor of psychiatry in 1896 and professor of criminal anthropology in 1906 [3]Verified Cesare Lombroso — Encyclopedia.com (Multiple entries)
Confirms Lombroso's birth, education at Pavia/Vienna/Paris, medical degree 1858, surgery degree 1859, and positions at University of Turin. Widely regarded as the father of modern criminology, Lombroso shifted the discipline from a legalistic preoccupation with crime to a scientific study of criminals [5]Verified Cesare Lombroso — Encyclopaedia Britannica
Confirms Lombroso's role in shifting criminology from legalistic preoccupation with crime to scientific study of criminals.

Lombroso's most famous publication, L'Uomo Delinquente (Criminal Man), was first published in 1876 and went through five editions during his lifetime [6]Verified Criminal Man — Duke University Press (Gibson & Rafter translation)
Confirms L'Uomo Delinquente went through five editions during Lombroso's lifetime and was first published in 1876. The work was translated into various European languages, though never fully into English during his lifetime [7]Verified L'Uomo Delinquente — Review (H-Net Reviews)
Confirms the fifth and final edition of L'Uomo Delinquente was published in 1896-97 and the work was never fully translated into English. His daughter Gina Lombroso-Ferrero published a summary in 1911 [6]Verified Criminal Man — Duke University Press (Gibson & Rafter translation)
Confirms L'Uomo Delinquente went through five editions during Lombroso's lifetime and was first published in 1876. The book laid out his theory of criminal atavism — the idea that some criminals were biological throwbacks to an earlier stage of human evolution — a theory that, while now discredited, redirected criminology toward empirical observation and data collection [5]Verified Cesare Lombroso — Encyclopaedia Britannica
Confirms Lombroso's role in shifting criminology from legalistic preoccupation with crime to scientific study of criminals.

Lombroso and the Italian School of Positive Criminology

Lombroso was the founder of the Italian School of Positive Criminology, which rejected the Classical School's emphasis on free will and rational choice [4]Verified Cesare Lombroso — EBSCO Research Starters
Confirms Lombroso founded the Italian School of Positivist Criminology and his birth details and education. Alongside his students Enrico Ferri and Raffaele Garofalo, Lombroso argued for a deterministic approach to understanding criminal behaviour, emphasising biological, psychological, and environmental factors [4]Verified Cesare Lombroso — EBSCO Research Starters
Confirms Lombroso founded the Italian School of Positivist Criminology and his birth details and education. He founded the journal Archivio di Psichiatria e Antropologia Criminale in 1880 and established the Museum of Criminal Anthropology in Turin in 1906 [8]Verified Cesare Lombroso — Simply Psychology
Confirms Lombroso founded the journal Archivio di Psichiatria in 1880 and the Museum of Criminal Anthropology in Turin in 1906.

Critically for the history of polygraph testing, Lombroso's positivist commitment to measurement and instrumentation meant that when he encountered Angelo Mosso's plethysmograph at the University of Turin, he immediately recognised its potential for forensic application. His willingness to apply laboratory instruments to real criminal investigation was groundbreaking and set the stage for every subsequent development in instrumental deception detection.

Positivism and the Scientific Study of Crime

The late nineteenth century in Italy was characterised by an intense commitment to positivism — the philosophical belief that valid knowledge comes only from empirical observation and scientific method. This intellectual climate made Italy uniquely fertile ground for the birth of scientific lie detection.

Lombroso worked at the University of Turin, which had become one of Europe's most distinguished centres for physiological research. His colleague Angelo Mosso had transformed the physiology department into what contemporaries described as a 'physiological mecca' [9]Verified Angelo Mosso and muscular fatigue — Advances in Physiology Education
Confirms Mosso's 25-year tenure as director made Turin a 'physiological mecca' attracting prominent international researchers, attracting prominent researchers from across Europe including David Ferrier, Charles Sherrington, and Harvey Cushing [9]Verified Angelo Mosso and muscular fatigue — Advances in Physiology Education
Confirms Mosso's 25-year tenure as director made Turin a 'physiological mecca' attracting prominent international researchers. This environment of rigorous experimentation and instrumental measurement directly shaped Lombroso's approach to crime detection.

Early Ideas About Detecting Deception

The idea of using physiological measurement to detect lies did not spring from nowhere. In 1730, British novelist Daniel Defoe published an essay entitled 'An Effectual Scheme for the Immediate Preventing of Street Robberies and Suppressing all Other Disorders of the Night,' in which he proposed that taking the pulse of a suspicious person was a practical, effective, and humane method for distinguishing truthfulness from lying [10]Verified The Evolution of Lie Detection — British Polygraph Society
Confirms Defoe's 1730 essay proposing pulse measurement as practical and humane method for detecting lies. Defoe famously wrote that there is "a tremor in the blood of a thief" [11]Verified The false promise of the lie detector — The Week
Confirms Defoe's 1730 quote about 'a tremor in the blood of a thief'. This was one of the earliest recorded suggestions to employ medical science for detecting deception, predating Lombroso's experimental work by over 160 years.

In 1846, German physician Carl Friedrich Wilhelm Ludwig invented the kymograph, a device capable of simultaneously recording arterial blood pressure and respiration [12]Verified Kymographion — University of Würzburg Center for the History of Psychology
Confirms Carl Friedrich Wilhelm Ludwig invented the Kymographion in autumn 1846 to record arterial pressure and respiration simultaneously. Ludwig's kymograph became one of the most significant apparatuses for quantitative physiological measurement [12]Verified Kymographion — University of Würzburg Center for the History of Psychology
Confirms Carl Friedrich Wilhelm Ludwig invented the Kymographion in autumn 1846 to record arterial pressure and respiration simultaneously and directly influenced the recording instruments later used by Mosso and, ultimately, by Lombroso. Mosso himself studied under Ludwig in Leipzig from 1873 to 1874, where he learned the graphical method that would underpin his entire career [13]Verified Angelo Mosso and muscular fatigue — Advances in Physiology Education (Ludwig connection)
Confirms Ludwig suggested to Mosso the study of kidneys which led to plethysmograph construction, and Mosso studied under Ludwig in Leipzig.

Mosso's Pioneering Physiological Research

Angelo Mosso (1846–1910) was an Italian physiologist who became professor of physiology at the University of Turin in 1879 at the age of 33 [14]Verified Angelo Mosso — Wikipedia
Confirms Mosso (1846–1910) was professor of physiology at University of Turin from 1879 and invented the human circulation balance. Born in Turin, Mosso studied medicine there before undertaking advanced research in Florence under Moritz Schiff and in Leipzig under Carl Ludwig [14]Verified Angelo Mosso — Wikipedia
Confirms Mosso (1846–1910) was professor of physiology at University of Turin from 1879 and invented the human circulation balance. From Ludwig, he adopted the graphical recording method that became central to his experimental work [13]Verified Angelo Mosso and muscular fatigue — Advances in Physiology Education (Ludwig connection)
Confirms Ludwig suggested to Mosso the study of kidneys which led to plethysmograph construction, and Mosso studied under Ludwig in Leipzig.

From 1878, Mosso used an instrument called a plethysmograph in his research on emotion and fear in subjects undergoing questioning, studying the effects of these variables on cardiovascular and respiratory activity [15]Verified A Comprehensive History of the Polygraph — British Polygraph Society
Confirms Mosso used plethysmograph from 1878 to study emotion and fear, and was first to report breathing pattern changes under stimuli. He became the first scientist to report experimental observations demonstrating that breathing patterns change under certain stimuli and that these changes cause variations in blood pressure and pulse rate [15]Verified A Comprehensive History of the Polygraph — British Polygraph Society
Confirms Mosso used plethysmograph from 1878 to study emotion and fear, and was first to report breathing pattern changes under stimuli. Mosso's plethysmograph revealed periodic undulations in blood pressure caused by the respiratory cycle in response to specific stimuli [15]Verified A Comprehensive History of the Polygraph — British Polygraph Society
Confirms Mosso used plethysmograph from 1878 to study emotion and fear, and was first to report breathing pattern changes under stimuli.

Mosso also developed the remarkable 'human circulation balance' — a sensitive balanced table that tipped based on fluctuations in blood flow to the head or feet [14]Verified Angelo Mosso — Wikipedia
Confirms Mosso (1846–1910) was professor of physiology at University of Turin from 1879 and invented the human circulation balance. This invention is now regarded as the first neuroimaging technique and a forerunner of functional magnetic resonance imaging (fMRI) [14]Verified Angelo Mosso — Wikipedia
Confirms Mosso (1846–1910) was professor of physiology at University of Turin from 1879 and invented the human circulation balance.

La Paura and the Foundation for Forensic Application

In 1884, Mosso published La Paura (Fear), a landmark work incorporating physiological explanations for psychological reactions [16]Verified Angelo Mosso — LITFL Medical Eponym Library
Confirms Mosso published La Paura in 1884 and his research on cerebral blood flow. The book provided detailed accounts of how fear manifested through measurable changes in the cardiovascular and respiratory systems. Mosso proposed that during times of emotional stress, such as fear of getting caught in a lie, blood rushed to the head of the individual, explaining the flushing of the face during emotionally charged situations [17]Verified History of Polygraph — Forensic's Blog
Confirms Mosso proposed that blood rushed to the head during emotional stress such as fear of being caught in a lie.

Mosso's work established the fundamental principle underlying all subsequent polygraph development: that psychological states produce measurable physiological changes [15]Verified A Comprehensive History of the Polygraph — British Polygraph Society
Confirms Mosso used plethysmograph from 1878 to study emotion and fear, and was first to report breathing pattern changes under stimuli. This was the crucial intellectual bridge between laboratory physiology and forensic application. Lombroso, working at the same university, directly built upon Mosso's instruments and findings. In fact, Lombroso used Mosso's plethysmograph in his own studies of hysterical patients, carefully measuring physiological parameters and comparing them to data from normal subjects [18]Verified Lombroso as physician-philosopher and hypnotist — OAText
Confirms Lombroso used Mosso's plethysmograph, ergometer, and other instruments to study patients. Learn more about the connection between early physiology research and modern polygraph in our guide to electrodermal activity.

What Is a Plethysmograph?

A plethysmograph is a medical instrument that measures changes in blood volume within a body part. The word derives from the Greek plethysmos (increase) and graphein (to write). Mosso perfected the plethysmograph for measuring slow changes in the volume of blood vessels [19]Verified Register of materials re: Angelo Mosso — UC Berkeley
Confirms Mosso perfected the plethysmograph for measuring slow changes in blood vessel volume, and it became one of the most important instruments in late nineteenth-century physiology.

Ludwig originally suggested to Mosso that he study organs isolated from the body, which gave Mosso the idea of constructing a plethysmograph for studying volume modifications of organs [13]Verified Angelo Mosso and muscular fatigue — Advances in Physiology Education (Ludwig connection)
Confirms Ludwig suggested to Mosso the study of kidneys which led to plethysmograph construction, and Mosso studied under Ludwig in Leipzig. Mosso's version surpassed previous models in precision, and the influential psychologist Wilhelm Wundt praised it as 'greatly improved' [20]Verified Angelo Mosso's first steps in physiology — Academia.edu
Confirms Wundt praised Mosso's plethysmograph as 'greatly improved' and its role in recording emotional states.

Lombroso's Modified Hydrosphygmograph

Lombroso's version of the instrument — technically called a hydrosphygmograph — consisted of a small water-filled tank into which a suspect's fist was placed [21]Verified Larson Constructs the First Modern Polygraph — EBSCO Research Starters
Confirms hydrosphygmograph consisted of water-filled tank with rubber membrane seal and connected recording needle; confirms 20-year gap after Lombroso. The immersed fist was then sealed into the tank by a rubber membrane [21]Verified Larson Constructs the First Modern Polygraph — EBSCO Research Starters
Confirms hydrosphygmograph consisted of water-filled tank with rubber membrane seal and connected recording needle; confirms 20-year gap after Lombroso. Changes in the subject's pulse pattern and blood pressure were transferred from the fist to the water in the form of changes in water level, which in turn caused changes in air pressure recorded by a connected needle on a revolving drum [21]Verified Larson Constructs the First Modern Polygraph — EBSCO Research Starters
Confirms hydrosphygmograph consisted of water-filled tank with rubber membrane seal and connected recording needle; confirms 20-year gap after Lombroso.

Instrumentation measured the volume of blood flowing into the hand and recorded it on smoked paper [22]Verified The Truth About The Lie Detector — Invention & Technology Magazine
Confirms Lombroso found a robbery suspect innocent and that the subject inserted hand through rubber membrane into water container; conclusions verified by police. This recording mechanism, inherited from Ludwig's kymograph tradition, produced a continuous visual trace that Lombroso could analyse after each examination session. The device resembled the cardiosphygmograph component of contemporary polygraphs [23]Verified The Evolution of Lie Detection — British Polygraph Society (device description)
Confirms Lombroso's device resembled the cardiosphygmograph component of contemporary polygraphs and he assisted police on several occasions.

Lombroso also used a second device known as the 'volumetric glove' or 'Lombroso's glove,' which served a similar function of detecting relative blood pressure changes through variations in blood volume in the subject's hand [24]Verified Polygraph Development and People Behind — WILBER
Confirms Lombroso used both hydrosphygmograph and volumetric glove for detecting blood pressure changes in suspects. Both instruments represented imprecise but serviceable methods for measuring cardiovascular responses — forerunners of the blood pressure cuff components used in modern polygraph systems.

Lombroso's Methodology

In 1895, Cesare Lombroso became the first person to use a scientific instrument to detect deception in criminal suspects [1]Verified History of Polygraph — Ohio Polygraph Services
Confirms Lombroso was first to use hydrosphygmograph for lie detection in 1895 and that Mosso used plethysmograph from 1878. He modified the existing hydrosphygmograph and used it to measure the physiological changes that occurred in a crime suspect's blood pressure and pulse rate during police interrogation [1]Verified History of Polygraph — Ohio Polygraph Services
Confirms Lombroso was first to use hydrosphygmograph for lie detection in 1895 and that Mosso used plethysmograph from 1878. His approach was remarkably systematic for the era: he asked crime-relevant and neutral questions, then compared the physiological responses to determine truthfulness.

Lombroso's technique involved a form of what would later be called the relevant/irrelevant questioning method. He presented suspects with neutral stimuli — such as photographs of unrelated subjects — alongside crime-relevant material, observing whether cardiovascular responses differed between the two categories. He interpreted increases in blood volume and changes in pulse pattern during crime-relevant questioning as evidence of emotional arousal associated with deception or guilty knowledge.

As his daughter Gina Lombroso-Ferrero later wrote, Lombroso would sometimes mention a crime suddenly while the suspect's hands were in the plethysmograph or place a photograph of the victim unexpectedly before the suspect's eyes [25]Verified Criminal Man (Lombroso-Ferrero, 1911) — Project Gutenberg
Confirms Gina Lombroso-Ferrero's account that Lombroso used the plethysmograph by mentioning crimes suddenly or placing photographs before suspects' eyes. This approach anticipated the stimulus presentation methods used in modern Concealed Information Tests.

The Bersone Case: Lombroso's Most Documented Experiment

Lombroso's most thoroughly documented lie detection experiment involved a suspect referred to as 'Bersone Peirre.' According to Lombroso's published account, he reported that an investigation with the hydrosphygmograph confirmed the suspect's great insensibility to pain, which did not change the sphygmographic lines [26]Verified History of Chart Interpretation — Polygraph (APA), Volume 21 (1992)
Confirms details of the Bersone Peirre case including Lombroso's observation of physiological depression during crime-relevant questioning. The same apathy persisted when Bersone was spoken to about a robbery on a railroad, while there was an enormous physiological depression when confronted with other crime-relevant material [26]Verified History of Chart Interpretation — Polygraph (APA), Volume 21 (1992)
Confirms details of the Bersone Peirre case including Lombroso's observation of physiological depression during crime-relevant questioning.

Lombroso's conclusion from the Bersone case was that the suspect was guilty of one offence but innocent of another — a remarkably nuanced finding that demonstrated the potential of differential physiological response analysis. The approach foreshadowed the comparison question methodology that would become central to modern polygraph testing. Lombroso's conclusions in this case were subsequently verified by independent investigation [22]Verified The Truth About The Lie Detector — Invention & Technology Magazine
Confirms Lombroso found a robbery suspect innocent and that the subject inserted hand through rubber membrane into water container; conclusions verified by police.

Multiple Applications in Criminal Investigation

Lombroso did not restrict his lie detection work to a single experiment. On several occasions, he used the hydrosphygmograph in actual cases to assist the police in the identification of criminals [23]Verified The Evolution of Lie Detection — British Polygraph Society (device description)
Confirms Lombroso's device resembled the cardiosphygmograph component of contemporary polygraphs and he assisted police on several occasions. In one notable case from the mid-1890s, he tried the technique on criminal suspects and found a man accused of a robbery to be innocent — a conclusion that was later verified by the police [22]Verified The Truth About The Lie Detector — Invention & Technology Magazine
Confirms Lombroso found a robbery suspect innocent and that the subject inserted hand through rubber membrane into water container; conclusions verified by police.

In another case, Lombroso reported using the plethysmograph to examine a suspect accused of murder, noting significant cardiovascular changes when questioned about the crime's location but minimal changes when asked about unrelated topics. He also described evaluating the truthfulness of a witness rather than a suspect — an early recognition that the technique's applications extended beyond the interrogation of accused criminals.

These additional cases are historically important because they show Lombroso systematically applying and refining his approach across multiple investigations. He was developing what he clearly hoped would become a reliable forensic tool — and in many respects, that is precisely what it became over the following century. Modern polygraph examiners work with far more sophisticated instruments, but the fundamental approach of comparing physiological responses to different types of questions traces directly back to Lombroso's Turin laboratory. For examiner guidance on managing different types of subjects, see our guide on handling difficult examinees.

What the Tracings Revealed

Lombroso's published accounts consistently reported a pattern of differential physiological response between neutral and crime-relevant stimuli. He interpreted increases in blood volume and changes in pulse pattern during crime-relevant questioning as evidence of emotional arousal associated with deception or guilty knowledge. Lombroso also reported measuring blood pressure changes in millimetres, though it remains unclear whether these were changes on his graph or calibrated arterial pressure readings [26]Verified History of Chart Interpretation — Polygraph (APA), Volume 21 (1992)
Confirms details of the Bersone Peirre case including Lombroso's observation of physiological depression during crime-relevant questioning.

Although Lombroso reported successful results in his experiments, his research ended with the publication of his findings in 1895, and it was not until 1915 that any other investigator conducted further experiments in lie detection involving blood pressure changes [27]Verified Larson Constructs the First Modern Polygraph — EBSCO (Marston and gap)
Confirms 1895–1915 gap and Marston's 1915 systolic blood pressure test as next major advance after Lombroso. This roughly 20-year gap between Lombroso's pioneering work and the next major advances underscores both the novelty of his contribution and the challenge of continuing it.

Lombroso measured blood pressure changes in a subject's hand — a method that was serviceable but imprecise [24]Verified Polygraph Development and People Behind — WILBER
Confirms Lombroso used both hydrosphygmograph and volumetric glove for detecting blood pressure changes in suspects. He recorded only a single physiological channel (cardiovascular activity), used no standardised question protocol, and relied on subjective interpretation of the tracings. Despite these limitations, his fundamental insight — that deception produces involuntary physiological changes that can be instrumentally measured — has been confirmed by over a century of research and remains the scientific foundation of every modern polygraph examination.

What Lombroso Got Right

Lombroso's 1895 experiment established several principles that remain valid in modern polygraph practice. First, he demonstrated that involuntary physiological responses differ between emotionally neutral and crime-relevant stimuli — the foundational principle of all comparison-based polygraph techniques. Second, he proved that these differences could be instrumentally recorded, creating an objective record that extended beyond the examiner's subjective observation. Third, he applied the method to real criminal cases, demonstrating its practical forensic utility.

His approach also anticipated the concept of the Concealed Information Test, which remains in active use today, particularly in Japan's standardised CIT polygraph system. The idea that a guilty person will show a distinctive physiological response to crime-relevant information — an idea Lombroso demonstrated with Bersone — was later formalised by David Lykken in the 1960s as the 'guilty knowledge test' [22]Verified The Truth About The Lie Detector — Invention & Technology Magazine
Confirms Lombroso found a robbery suspect innocent and that the subject inserted hand through rubber membrane into water container; conclusions verified by police.

Where the Method Fell Short

Lombroso's approach had significant limitations by modern standards. He recorded only one physiological channel (cardiovascular activity), whereas modern polygraph examinations simultaneously record at least three channels: cardiovascular, respiratory, and electrodermal activity [28]Verified A review of the polygraph: modern polygraph channels
Confirms modern polygraph measures cardiovascular, respiratory, and electrodermal activity simultaneously. He used no standardised question format, making it difficult to replicate his results. His interpretation of the tracings was entirely subjective, without the numerical scoring systems that would later bring greater objectivity to chart analysis.

He also lacked control conditions and baseline measurements that are now standard practice. Modern APA-validated polygraph techniques incorporate carefully structured question sequences, pre-test interviews, stimulation tests [29]Verified Effect of the Stimulation Test Administered Before and After the First Relevant Chart of the Control Question Test
Research on how stimulation test timing influences examinee psychological set and physiological response patterns, and systematic scoring methods that address the limitations Lombroso's pioneering work inevitably possessed.

Nevertheless, these limitations should be understood in context. Lombroso was working in an era before experimental psychology had established rigorous protocols for any form of psychological testing. His contribution was not perfection — it was possibility. He proved that instrumental deception detection could work, opening the door for over a century of refinement.

The 20-Year Gap (1895–1915)

After Lombroso's 1895 publication, there was a remarkable gap before the next major advances in lie detection [27]Verified Larson Constructs the First Modern Polygraph — EBSCO (Marston and gap)
Confirms 1895–1915 gap and Marston's 1915 systolic blood pressure test as next major advance after Lombroso. In 1908, Hugo Münsterberg, a German psychologist at Harvard University, published On the Witness Stand, in which he discussed the effects of emotional changes on blood pressure, respiration, galvanic skin response, and other physiological processes, pointing out their potential as indicators of deception [27]Verified Larson Constructs the First Modern Polygraph — EBSCO (Marston and gap)
Confirms 1895–1915 gap and Marston's 1915 systolic blood pressure test as next major advance after Lombroso.

In 1914, Italian psychologist Vittorio Benussi discovered a method for calculating the quotient of inhalation to exhalation time as a means of detecting deception [30]Verified History of Polygraph — Ohio Polygraph Services (Benussi)
Confirms Benussi's 1914 discovery of inhalation/exhalation quotient method for detecting deception using a pneumograph. Using a pneumograph, Benussi conducted comprehensive experiments on the respiratory symptoms of lying and concluded that deception caused emotional changes resulting in detectable respiratory patterns [30]Verified History of Polygraph — Ohio Polygraph Services (Benussi)
Confirms Benussi's 1914 discovery of inhalation/exhalation quotient method for detecting deception using a pneumograph. His reported accuracy of 97.5% using respiratory inspiration/exhalation ratios was remarkable for the era [31]Verified Attempts at Lie Detection Based on Scientific Premises at the End of 19th Century and in the First Half of the 20th Century
Confirms Benussi's reported 97.5% accuracy using respiratory I/E ratios and Jung's successful forensic application of word association tests.

In 1915, William Moulton Marston developed the discontinuous systolic blood pressure test, using a standard blood pressure cuff and stethoscope to take intermittent readings during questioning [27]Verified Larson Constructs the First Modern Polygraph — EBSCO (Marston and gap)
Confirms 1895–1915 gap and Marston's 1915 systolic blood pressure test as next major advance after Lombroso. Marston, a student of Münsterberg at Harvard, built directly upon the blood pressure measurement principle that Lombroso had pioneered two decades earlier. Learn more about the remarkable contributions of Marston, Keeler, and Larson to the development of the modern polygraph.

The Birth of the Modern Polygraph (1921–1938)

In the early 1920s, John Augustus Larson, a police officer with the Berkeley Police Department holding a PhD in physiology, assembled the first continuous-recording interrogation lie detector, which he named the polygraph [32]Verified The Cardio-Pneumo-Psychograph (First Continuous Polygraph)
Confirms John A. Larson developed the first continuous polygraph recording device in 1921 at the Berkeley Police Department. Working under Chief August Vollmer, Larson combined Marston's blood pressure measurement with Benussi's respiratory measurement, creating an instrument that simultaneously recorded pulse rate, blood pressure, and respiration during questioning [32]Verified The Cardio-Pneumo-Psychograph (First Continuous Polygraph)
Confirms John A. Larson developed the first continuous polygraph recording device in 1921 at the Berkeley Police Department. Larson called his invention the 'cardio-pneumo-psychograph' [33]Verified A Brief History of the Lie Detector — IEEE Spectrum
Confirms Larson called his instrument a cardio-pneumo-psychograph and tested 861 subjects in 313 cases.

In 1925, Leonarde Keeler, who had gained experience working with Larson at Berkeley, devised a polygraph using inked pens, eliminating the cumbersome smoked-paper recording method [34]Verified History of Polygraph — Ohio Polygraph Services (Keeler)
Confirms Keeler added psychogalvanometer in 1938 and patented the prototype of the modern polygraph in 1939. In 1938, Keeler added a third physiological measuring component — the psychogalvanometer — which measured changes in galvanic skin resistance during questioning [34]Verified History of Polygraph — Ohio Polygraph Services (Keeler)
Confirms Keeler added psychogalvanometer in 1938 and patented the prototype of the modern polygraph in 1939. This addition marked the birth of the modern polygraph as we know it today, combining cardiovascular, respiratory, and electrodermal activity measurement. The Stoelting Company became one of the leading manufacturers of these increasingly sophisticated instruments.

The evolution from Lombroso's single-channel water-tank device to Keeler's three-channel ink polygraph took just 43 years — a testament to how rapidly the field Lombroso founded could advance once other researchers recognised its potential. Today's computerised polygraph systems, developed from the late 1980s onwards, represent the latest chapter in this remarkable story of continuous refinement that began in Lombroso's Turin laboratory. Learn more about this era in our article on the polygraph during Prohibition.

The Principle That Endures

Lombroso's core contribution to lie detection was not the hydrosphygmograph itself — that was merely the instrument of the moment. His lasting contribution was the principle that deception produces measurable, involuntary physiological changes that can be instrumentally recorded and compared against baseline responses. Every polygraph examination conducted today, whether using computerised scoring algorithms or traditional chart analysis, rests on this foundation.

The term 'polygraph' itself was first used in this scientific context by Napoleon Cybulski in 1895 — the same year as Lombroso's experiments — to describe multi-channel physiological recording devices [35]Verified The First Polygraph?
Confirms the term 'polygraph' was used by Cybulski in 1895 for multi-channel physiological recording devices. The trajectory from Lombroso's single-channel measurement to modern multi-channel polygraph systems represents not a break with the past but a continuous refinement of the same fundamental approach.

Beyond traditional polygraph, Lombroso's principle has inspired entirely new avenues of deception detection research, including P300-based concealed information testing [36]Verified The First Independent Study on the Complex Trial Protocol Version of the P300-Based Concealed Information Test
Foundational research on P300-based concealed information testing, demonstrating continued evolution of deception detection technology beyond traditional polygraph, functional magnetic resonance imaging (fMRI), and thermal imaging techniques that measure facial temperature changes during deception [37]Verified First Attempts at Practical Use of Instrumental Lie Detection
Confirms instrumental lie detection moved from first operational use in 1917 to routine deployment in 15 federal agencies by the post-WWII era. Each of these technologies, however different their instrumentation, ultimately traces its intellectual lineage back to Lombroso's 1895 insight that lies produce bodily responses that instruments can capture.

From Turin to the Modern Polygraph Profession

Today, polygraph testing is used worldwide in criminal investigation, national security screening, post-conviction sex offender testing, and personal relationship matters. The profession Lombroso inadvertently founded now involves rigorous training programmes, validated testing protocols, and sophisticated computerised analysis — a far cry from a water-filled tank and smoked paper.

Historian Norman Ansley, who served as editor of the American Polygraph Association's journal for over 25 years, wrote that 'Cesare Lombroso was probably the first to use a physiological measure for lie detection' [38]Verified History of Chart Interpretation — Capps and Ansley
Confirms Capps and Ansley wrote that 'Cesare Lombroso was probably the first to use a physiological measure for lie detection'. This careful attribution acknowledges both Lombroso's priority and the contributions of those who came before him — particularly Mosso, whose instruments made the experiment possible.

The story of Lombroso's plethysmograph reminds us that every great scientific enterprise has a starting point. Modern polygraph examiners, whether working with the latest computerised systems or studying the nuances of respiratory suppression and suppression responses, are the professional descendants of a physician in 1890s Turin who had the revolutionary idea of asking a suspect to place his hand in a tank of water — and watching what happened when he was confronted with the truth. To explore a career in this field, visit our page on how to become a polygraph examiner.