Colored chemical tests for arsenic in a nineteen-century chemistry textbook. From Jean-Louis Lassaigne. 1844. Tratado completo de química … Madrid.
Forensic Scientists
15th February 2024
by Jose Ramon Bertomeu Sànchez
Created at:
15th February 2024
Jose Ramon Bertomeu Sànchez
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Colored chemical tests for arsenic in a nineteen-century chemistry textbook. From Jean-Louis Lassaigne. 1844. Tratado completo de química … Madrid.

In different passages of his books, Friedrich Nietzsche denounced the general neglect of smell in Western epistemology. In the following quotation, from his Twilight of the Idols (1889), he praised the power of noses as “fine instruments of observation” and he compared the delicate sensibility of his nose for detecting “minimal differences in movement” which were impossible to be registered by spectroscopes:And what fine instruments of observation we have in our senses! This nose, for example, of which not one philosopher has yet spoken in reverence and gratitude, is nevertheless actually the most delicate instrument we have at our command: it can register minimal differences in movement which even the spectroscope fails to register. (Nietzsche 1998, 12)

Spectroscopes had been introduced in mid nineteenth century and they were employed in subsequent decades to discover for multiple purposes in science and medicine from the detection of minute quantities of new chemical elements in minerals to the spectral analysis of light emissions of distant planets and starts and also for the study of the colorant principle of blood (hemoglobin). The favorable comparison between the olfactory organ and a powerful scientific instrument might be surprising nowadays, but it aligns with the significance of smelling and tasting in nineteenth-century chemistry and medicine. During this period, physicians frequently utilized their "sensuous technology" in routine clinical practice, heavily relying on observations through seeing, touching, listening, and smelling. Similarly, the sensuous technology of chemists and pharmacists was equally extensive in their research at the laboratories, when performing analysis of chemicals or drugs (Bynum and Porter 1993).

And yet, one can agree with Nietzsche in the scarce (or even negative) value attributed to the sense of smell in most of the studies on history and philosophy of science. An example of this trend is the French philosopher Gaston Bachelard who regarded odors as one of the most dangerous sources of “substantialisme”, one of the main “epistemological obstacles” in the development of science, particularly important in the case of chemistry. According to Bachelard, the development of modern scientific mind involved the necessary “desensualisation of chemical knowledge” by means of an increasing role of quantitative approaches (physical laws, mathematics) and scientific instruments, from balances to spectroscopes. (Bachelard 1993, 139–40; Le Guérer 1998, 201–3).

Feelings and Noses

Some historians have affirmed that the so-called “Chemical Revolution” at the end of the eighteenth-century was the crucial moment for the “death” of the “sensuous chemists” thanks to the advent of new scientific instruments and forms of objectivity involving a growing role for quantitative measurements. In an influential paper, Lissa Roberts claimed that the eighteenth-century “sensuous technology” of chemists was largely replaced by scientific instruments producing quantitative data and graphics. Even if smell and taste remained active in laboratory practice, they played a decreasing role as sources of reliable scientific observations (ROBERTS 1995). This idea resonates with the once popular thesis of the progressive “deodorization” of society and the “decline” in the cultural meaning of smell during the nineteenth century (Corbin 1982; Classen and Howes 1994; Jenner 2011). 

New studies have revisited the idea of “desensualition” while showing that the uses of senses (including smell) remained very important after the so-called “Chemical Revolution” at the end of the eighteenth-century. For instance, a recent review of the papers published at the most important late eighteenth-century chemistry journal (Annales de chimie), which is commonly regarded as one of the main vehicles of the new chemistry, confirms that smell, vision and taste was extensively employed by chemists in early nineteenth-century in the identification of substances and the study of chemical processes, in many cases connected to practical purposes related to public health, quality of food, analysis of water or healthiness of air (Cornu 2023).

The arrival of new instruments (balances, eudiometers, microscopes, polarimeters, colorimeters, etc.) and new liquid tests with reagents did not involve the end of sensorial experience.  On the contrary, the senses (colors, smells, flavors) remained as a fundamental resource for chemists, sometimes intermingled or competing with other forms of empirical data obtained by means of complex instruments or chemical analysis. The recognizance of color nuances, peculiar scents and particular flavors largely remained a crucial part of the work of chemists in a disparate array of areas such as food quality control, chemical analysis, public health, perfume industry or forensic science. And many controversies took place on the subjective nature of this data, the replicability with different experimenters or the tensions with other forms of evidence in areas such as public health (Kiechle 2017), food quality control (Atkins 2010) or potable water supply (Spackman and Burlingame 2018). Moreover, with the advent of new experimental approaches, the new studies on the “odorant principles” were developed in different contexts, from early nineteenth-century studies on the physiology of taste (Brillat-Savarin 1826) or on the classification of smells and the anatomy of olfactory organs (Cloquet 1821) to the twentieth-century studies on the chemical nature of olfaction, studies on the production of food additives and artificial flavors or the more recent attempts to create “chemical noses” which could compete with the olfactory organs of experts and connoisseurs (Reinhardt 2014; Gennermann 2023; Shapin 2012).

The mentioned examples confirm that a growing number of studies have been devoted to the role of senses (including smell) in the development of science and medicine following the increasing scholarship on the cultural history of the senses (Jenner 2011; Tullett 2023). Focusing on the detection of bloodstains in nineteenth-century, I explore the challenges associated with relying on sensory information (not only smell) as credible evidence in both laboratories and courtrooms. To begin, I present an overview of the challenges associated with detecting bloodstains in the nineteenth century, focusing on the method introduced by Jean-Pierre Barruel, which relied on the scent generated when bloodstains were treated with sulfuric acid. I contextualize this method within the broader landscape of chemical and medical investigations into the “odorant principles” of both plants and animals. In the subsequent section, I review various trials where Barruel's method was employed, detailing the controversies that unfolded in both medical academies and courtrooms. Finally, I examine the reception of Barruel's method in different European countries until the mid-nineteenth century. Through this analysis, I demonstrate that the challenges faced by the smell test mirrored those encountered by other chemical and microscopic technologies employed for the detection and differentiation of various types of bloodstains.

While the appearance of freshly spilled blood is generally recognized, discerning whether a stain on clothing, knives, glasses, or wood discovered at a crime scene is genuinely attributable to blood poses a far greater challenge. Dr. William D. Sutherland, who authored a comprehensive book on bloodstains at the outset of the twentieth century, remarked the diverse nuances of color, ranging "from dull red, through reddish-brown, to a dirty grey," which he attributed to different conditions at the crime scene, including factors like humidity, rain, and dust (Sutherland 1907). This variability is just one of the difficulties involved in distinguishing genuine bloodstains from other substances in crime scenes. In addition, forensic experts faced the intricate task of providing judges with additional information concerning issues such as whether the blood in question originated from a human or an animal, for how long the blood had been present on knives or clothes, or whether the blood found on various items belonged to the victim or the defendant. Nineteenth-century experts could only provide partial answers to some of these questions and with different degrees of certainty.  

Owing to the pivotal role of bloodstain evidence in establishing violent crimes, errors in its detection had profound consequences, potentially leading to the wrongful release of murderers or, even graver, the conviction of innocent defendants. The tension between the rigorous standards of proof demanded in murder trials and the uncertainty surrounding the detection of bloodstains became a cause for concern among many forensic doctors and judges in the nineteenth century. By the mid-nineteenth century, predominant methods for detection relied on chemical tests and microscopic observations. These methods underwent continuous refinement and innovation, sometimes prompted by unforeseen challenges encountered at crime scenes, in other cases thanks to new research on the chemical ingredients of blood, advancements in chemical analysis or enhancements in microscope lens technology. Judges and lawyers could ask experts on a large range of questions, occasionally giving rise to controversies within courtrooms.

One of the methods for detecting bloodstains was introduced at the end of the 1820s by Jean-Pierre Barruel (1780-1838), the head of the laboratory of the prestigious Paris Faculty of Medicine during the first third of the nineteenth century. Son of a grocer, he started his career as laboratory under the supervision of famous chemists such as Antoine-François Fourcroy or Nicolas Vauquelin. He occasionally published papers on topics related to the analysis of food and water and frequently collaborated with Mateu Orfila (1787-1853), professor of chemistry at the Paris Medical Faculty and one of the most famous French forensic doctors during the 1820s and 1830s. Barruel also participated in some of these trials and, being requested by the judge to distinguish between human and animal bloodstains, he imagined a new test based on smell (Bertomeu Sánchez 2019).

According to Barruel’s account, his smell test emerged from his regular work as laboratory assistant. Both Fourcroy and Vauquelin were involved in research on the ingredients of blood. Apart from reagents and glass tubes, chemists commonly employed the senses (including smell) in their experimental research. Many eighteenth-century works were focus on the “odorous principle” of blood, which was regarded by many authors as analogous to the principles (“esprits recteurs”) producing the aroma of plants and being employed in the pharmacy and perfume industry. Contrary to being an epistemological obstacle, as posited by Bachelard, research into these aromatic principles yielded new data on pertinent subjects within the realms of chemistry, medicine, and botany. For instance, significant advancements unfolded during the early nineteenth century stemming from research into the odorant principles of plants or the flavoring principle of meat (“osmazome”), along with different conceptualizations of vital forces and organic matter, in the quest for innovative technologies or new products in the realm of perfume or food production (Levitt 2023; Spary 2014, 229–31).

Experimental research on the smell of blood was regarded as being potentially fruitful for medical purposes, so it attired the interest of physicians and apothecaries in the eighteenth century. For instance, the French apothecaries Antoine-Augustin Parmentier (1737-1813) and Nicolas Deyeux (1745-1837) performed experiments aiming to shed light on the alterations of blood during different diseases. This work was followed by Antoine Fourcroy, who summarized these studies in his influential textbook on chemistry published in 1800. He also largely reported the studies on the smell of blood and, even if he doubted the existence of a particular principle, he noted that the odor of blood was non-existent in old people and eunuchs, weaker in children and women, and more pronounced in males after puberty (Bertomeu Sánchez 2015). 

According to Barruel’s account, he was helping Nicolas Vauquelin in his experiments on the colorant principle of blood when the idea of the smell detecting test first came into his mind. In order to extract this principle, the clot of beef blood was immersed in diluted sulfuric acid and heated. On one occasion, Barruel was struck by the “odor of beef which emanated from it”. Some years later, he helped Orfila in his forensic investigation concerning a case of suicide by means of opium.  In order to detect morphine in blood, Barruel added diluted sulfuric acid to the blood found in victim’s clothes and he perceived the “odor of man’s sweat”, so intense that Barruel was “compelled to leave the laboratory”. Then, Barruel started a large number of similar experiments with blood samples from human and non-human (pigs, sheep, cows, etc.) origin. Relying on these experiments, he concluded that the blood of each animal species had a distinctive “odorous principle” (“principe odorant”) which could be released by means of sulfuric acid, so that “it was not only possible but also easy enough” to recognize the smell of the animal. He even claimed that he could distinguish between the smell of male and female blood (Barruel 1829).

Hence, Barruel's innovative smell test was firmly grounded in prior investigations into the fundamental principles of blood and the odorant principles. These studies were pioneered by professors who as Barruel were affiliated with the renowned Faculty of Medicine, a distinguished medical institution that drew students from across the globe at that time. Moreover, analytical chemistry in the nineteenth century relied on liquid tests typically conducted in small glass tubes. The substances under analysis were subjected to a series of reagents to induce specific precipitates or colored solutions, the subtle nuances of which were discernible only to well-trained observers. Training on these relevant color nuances in the dominant black-and-white culture of chemistry textbooks was difficult. In the second half of the nineteenth-century, the arrival of new instruments, such as the spectroscopes mentioned by Nietzsche, involved more relevance of color in chemistry. Spectroscopy was “extraordinarily visually oriented” field whose practitioners relied on spectral lines as fundamental information for analyzing mixtures, detecting poisons and discovering new elements (Hentschel 2002; 2014).

Taste and smell also played a substantial role in chemical tests while facing similar uncertainties, controversies and replication problems. Smell tests were employed to identify several well-known poisons such as arsenic (the garlic-like smell when sublimated), lead acetate (odor similar to vinegar) and hydrocyanic acid (smell of bitter almonds). Many decades before Nietzsche, one of the most famous nineteenth-century toxicologists, Mateu Orfila praised the role of noses as the most sensitive tool for detecting poisons such as hydrocyanic acid. He even advantageously compared the sensibility of the olfactory organ with the most advanced reagents employed at his times for detecting hydrocyanic acid. He concluded that “the olfactory organ and the silver nitrate” were the “most sensible means of detecting atoms of this acid” (Orfila 1829, 492).

Colored chemical tests for arsenic in a nineteen-century chemistry textbook. From Jean-Louis Lassaigne. 1844. Tratado completo de química … Madrid.

The evidential significance ascribed to colors, odors, and tastes was contingent upon various factors, including the nature of the substances under scrutiny, the reagents employed in testing, the laboratory resources and the expertise of the analysts. Take, for instance, alkaloids and other organic compounds, for which liquid tests and colored reagents offered limited utility for chemical analysis or forensic toxicology until the mid-nineteenth century. Chemists, in such cases, relied on distinctive odors or flavors, such as the unmistakably bitter taste of strychnine. Conversely, despite the availability of highly sensitive tests in the 1830s, numerous nineteenth-century physicians persisted in using the garlic-like scent of arsenic alongside old liquid tests. Even with the introduction of new instruments, analytical chemists continued to employ test-tube glassware, standardized color reagents, and a broad range of tacit knowledge concerning the subtleties of colors, scents, and flavors. By the midpoint of the century, many of these tests were organized into chemical groups, involving diverse protocols that incorporated the use of the disagreeable hydrogen sulfide, obtained from Kipp’s apparatus. This substance was employed in the initial phases of the separation process, alongside other reagents that produced distinct colors and flavors (Szabadvary 1960; Baird 1993; Homburg 1999).

Jean-Pierre Barruel was trained in the management of this universe of colors, scents and flavors. He employed his trained eye as well as olfaction and gustation in his on regular work at the laboratory of the Paris Medical Faculty and in his forensic investigations when he was appointed as expert in criminal trials. Thus, he was acquainted of the problems surrounding the use of senses in the production of chemical facts and legal evidence. Besides the research developed with his colleagues on the odorant principle of blood, the questions raised by lawyers and judges encouraged forensic doctors like Barruel to perform new experiments in order to refine their methods. The trials were also a source of unique clinical and chemical information for this purpose (Bertomeu Sánchez 2019; Burney 2006).

In his first account of this smell test, Barruel offered practical details concerning the correct performance of the test as well as directions to both judges and experts concerning the different situations to be found in crime scenes. For instance, he warned that his method has dry bloodstains found in clothes only for the first two weeks, so he urged judges to ask the experts to perform the experiments as soon as possible. Barruel also advised that the experts should be trained in their sense of smell (‘l'éducation de leur odorat’) before performing the experiment properly. He likewise warned that the procedure had to be practiced several times with pure samples (human and animal blood) before making the actual test with the suspicious substances (Barruel 1829).

The first trial in which Barruel’s test was employed took place in 1829. The defendant, Pierre-Augustin Bellan, a Parisian butcher whose wife's bloodily body was found in August 1828. The examining magistrate conducted a search of his house and found a shirt apparently stained with blood, but Bellan argued that the blood found in his clothes was not from his wife but from pigs and cows he had slaughtered during his work at the butcher shop. It was the right time for Barruel to employ his new method.  With the help of two Parisian pharmacists, he performed the analysis of the bloodstains in mid-March 1829 in the laboratory of the Faculty of Medicine.  After applying chemical reagents to confirm that the stains were really produced by blood, they trained their noses before performing the smell test. They stained various clothes with blood from both (pig and ox) animal and (male and female) human origins. They exposed the stained clothes to air for several days in order to imitate the conditions in the actual crime scene. Subsequently, each expert separately tested every bloodstain dipping it in water, adding sulfuric acid and smelling the scent.

All of them noted the pig blood gave off "a very marked and strongly unpleasant odor, in which the odor of the pig seemed to be distinguishable", while the ox blood offered "a less marked odor" analogous to that perceived in the stables. The male blood generated a "very marked odor, like fat and analogous to that of sweat", and that of the female "a slightly less sour, not unpleasant odor". Then, after training their olfactory organs in this way, the experts carried out the analysis of the bloodstains found on the defendant's shirt. The two pharmacists declared that they perceived “a sour, not unpleasant odor” but they did not identify it with the female blood they tested several days ago. On the contrary, Barruel affirmed that this odor was characteristic of female blood, even if he cautiously presented his results in court. With the help of other circumstantial evidence, the butcher was eventually convicted and given the death penalty (Bertomeu Sánchez 2015).

The Bellan trial highlighted several challenges encountered by olfactory-based evidence in courts. On one hand, replicating the evidence proved difficult due to the inherent variability of noses and the diverse olfactory expertise that could be improved by training. Experts also came to realize that the scents produced by the test could vary significantly depending on the animal or human origins, maybe influenced by factors such as age, diet, or health condition. As some critics pointed out, the extent of divergence was unknown, and under specific conditions, marked differences could exist between blood samples from the same biological species. Even more perplexing, certain noses might perceive blood from different species as similar and produce false positives. The idea was nicely expressed in a German journal, where it was affirmed that for detecting such nuances “a special Barruel-like nose was necessary” (“eine besondere, Barruel’sche Nase”) (Ritter 1860, 41).

Barruel, undeterred by the challenges posed by evidentiary issues, persisted in adhering to the guidance of his nose in the murder trials where he was called upon as an expert witness during the 1830s. In one of his last apparitions in court, he was asked to identify the bloodstains found on a bed linen. As on previous occasions, he cautiously answered that he thought it was female blood but he could not “affirm it positively” because the linen was dirty. However, when the judge asked whether ‘female blood was distinguishable from male blood’, he answered:

Very easily, your Honor. In all animals, the female blood has very different features from those of the male blood. On white-as-snow linens, I would distinguish with total certainty, not only the blood of a woman, but the different species of female blood, young or old, blonde, brunette or redhead. I have compared and analyzed more than two thousand blood samples, and I have trained my sense of smell fairly well, so as to be sure not to make mistakes. (Gazette des Tribunaux, 1 February 1838).

Predictably, Barruel's assertions regarding the discerning capabilities of his nose faced serious challenges in both courtrooms and medical academies. The issue was extensively discussed at the Paris Academy of Medicine, and it became a focal point in various murder trials conducted in the 1830s. Numerous experts attempted to apply the technique, often with unsuccessful outcomes, and in other instances, the results were inconclusive or contradictory. Nevertheless, judges and lawyers persisted in requesting this test, as it stood as the sole available method at that time to differentiate between human and animal blood.

In legal debates, the episode was invoked to discuss the admissibility for expert testimony in courts. Barruel faced accusations of employing methods that lacked scientific consensus, leading some experts to reject the results obtained by his test, while others admitted them with reservations. Additionally, given the contentious nature of the smell test's status among courtroom experts, it had the potential to sway public opinion against judges who rendered a death penalty verdict based on such dubious evidence. Other critics also remarked the risk of relying on the alleged “infallibility of Barruel’s or any other chemists’ sense of smell”, particularly in murder trials involving dead penalty.  One of first, and most persistent, critic of Barruel’s test was François-Vicent Raspail who argued in that direction:

Assuming that the odoriferous characteristics of blood are, as Barruel claims, likely to be recognized with some certainty, the experiments conducted by this chemist are too few in number and insufficiently connected to be accepted as a reliable source of legal evidence. [Barruel] has only operated on a dozen animal species; and who can certify in advance that, among the many species listed in zoological catalogs, there cannot be some whose blood, when tested with sulfuric acid, gives off an odor similar to that of human or female blood? If, out of one hundred animals, one has tested ninety-nine, I would still be entitled to argue in courts, until proven otherwise, that the hundredth might thwart the reagents. (Raspail 1829, 139–40)

In this manner, Raspail delved into some of the contradictions between law and science, particularly the irreversible consequences of judicial verdicts as opposed to the provisional nature of scientific research. This theme could be extrapolated to other evidentiary technologies for detecting blood, such as chemical tests or microscopy. Even if all known sources of error were taken into account, who could definitively assert that subsequent studies would not reveal other previously unknown factors leading to misleading results or false positives? Following a death sentence, how could the severed head of the defendant be restored once the error in the expert report was eventually acknowledged? Raspail's skeptical arguments regarding scientific evidence were employed in numerous murder trials and resonated with the mounting concerns about judicial errors during the nineteenth century. 

The public controversy was advantageously employed by the defense in subsequent trials. In 1839, just some months after Barruel’s death, his son Jean-Joseph-Ernest Barruel was requested to examine the stains found in the defendant’s clothes during a high-profile murder trial. The defendant claimed that it was his own blood and he asked the experts to prove it because he had been told that chemists could distinguish the blood let from different individuals. Barruel’s son was unable to accept the challenge. He affirmed that his father’s method could only be employed when there was a substantial quantity of blood, which had remained for only a few days in the clothes. In this case, the bloodstains were too small and the cloth very dirty, thus making impossible to obtain conclusive results. He employed this examples to argue that the smell test could be employed for the development of science but it could not offer the reliable evidence needed in criminal investigations (Bertomeu Sánchez 2015). 

Jean-Pierre Barruel (1780-1838), funerary monument at the Paris Montparnasse cemetery.

And yet, the smell test was employed in courts and laboratories for several decades after the death of his creator. In 1829, the professor of physics at the University of Bologna, Francesco Orioli (1785-1856), who had also studied law in Rome, and his colleague Gaetano Sgarzi (1795-1866), professor of pharmacy at the same University praised Barruel’s test as a method useful not only for legal medicine but also in medical diagnosis because they affirmed that different illnesses could be recognized by the changes produced in the odorous principle. Introducing several experimental improvements, they performed the test on different animals and humans affected by different illnesses. In order to face the problem of replicability, they suggested to employ sealed vessels in which the odorous principle could be preserved for weeks and tested by various experts or even judges and lawyers during trials (Orioli and Sgarzi 1829).

Ten years later, the doctor Corrado Taddei de Gravina tested a large number of samples of blood from animals (cows, birds, horses, goats, hares, etc.) and men and women. He also concluded that concluded that an odoriferous principle, identical in all individuals of the same species, existed in the blood of vertebrate animals. Consequently, he affirmed that the distinctive scent of human blood could be employed to difference between human and other mammal’s blood in the forensic investigation of bloodstain. However, the test could not be employed to recognize a particular group of individuals (for instance, men and women as Barruel claimed) because the odorant principle remained similar in each specie regardless of age, sex, body constitution, lifestyle, health or illness, dietary habits, consumption of drugs, or even the state of pregnancy (Gravina 1840).

In Berlin, a medical association offered a prize in 1846 for the physicians who could enhance methods for detecting and distinguishing different types of bloodstains. The winner was the doctor Bernhard Ritter who concluded that no method was available to discern between human and non-human blood with absolute certainty. He thought that the most reliable information was provided by the combination of the chemical (smell test) and microscopic examination methods (Ritter 1860, 74–75). Also in the late 1840s, with the help of six students, the professor Carl Schmidt performed further experiments on the odorant principle of different species of mammals, birds and amphibians. While some kinds of blood (sheep, cat, etc.) were easily detected with accuracy by all the experimenters, in many other cases they diverged in their conclusions or expressed doubts regarding the perceived scents (Schmidt 1848, 19–21). Similar experiments were performed elsewhere in Europe. In mid-nineteenth-century Paris, the author of a medical thesis on bloodstains affirmed that it was “evident that the blood of every animal species owns a particular odor” because “the blood contains […] an odorous principle which is particular to each animal”. And he suggested new ways to release this smell by means of new reagents, even if, like most of his forerunners, he was cautious about the possible uses in legal medicine (Humbert 1856).

In Britain, the method was known and practiced, but its applications in legal medicine faced extensive criticism. In his influential textbook on legal medicine, forensic doctor Alfred S. Taylor provided a concise overview of the test. However, he did not recommend it because it required experts to have a “sense of smelling” so “acute” as to allow them “to state with undeniable certainty, from what animal the unknown blood had really been taken”. And he added: “Any evidence short of this would not be received in an English court of law; for it is considered better not to decide at all, than to decide on principles which are exposed to unavoidable fallacy” (Taylor 1844, 333). Taylor’s remarks suggest that Barruel’s test was employed as an example of the risks of the inquisitorial French legal system. A doctor from Ewell (Surrey), reviewing new methods for the detection of blood stains for the Medical Times in 1850, wrote: 

The recognition of human blood by the odour evolved on adding strong sulphuric acid, and even in its distinctive peculiarity in each sex, may be a possibility to the acute olfactories of our French neighbors, but to our more obtuse sensibility, it probably would not be practicable; and, at any rate, evidence based thereon would not readily be accepted in an English court of justice. (Butler 1850).

Another problem for the smell test was the increasing role of microscopes in medical practice during the first half of the nineteenth-century. During the 1840s and 1850s, microscopists developed many ways to deal with bloodstains in the particular circumstances of legal medicine practice. By the middle of the nineteenth century, the combination of chemical tests and microscopic observations offered new possibilities for detecting bloodstains. The new test introduced by Ludwig Teichmann involved the formation of distinctive crystals (by means of acetic acid) which were viewed under the microscope. However, the fiery controversies concerning the reliability of this and other similar tests in distinguishing human from non-human blood did not disappear from courts during all the second half of the nineteenth century (Golan 2000). 

By the end of his life, one of the most famous German forensic doctors, Johan Ludwig Casper (1796-1864) summarized in his authoritative textbooks the different methods based on chemical tests and microscopic observations and, like many of his forerunners, remarked that “all had proved to be too complicated and too uncertain to be practically useful”. He also mentioned the smell test:

Much attention has rightly been directed to Barruel's pretended discovery of the power of distinguishing human blood from that of animals by means of the peculiar odor evolved by the action of pure sulfuric acid. But if it be hazardous in medico-legal cases to admit proof depending on a nice distinction of colors, it is doubly so to employ in such cases the sense of smelling as a criterion, for there is no sense more liable to greater individual differences than this is, and indeed Barruel's method has been found wanting when tested by experiment. (Casper 1856, 140)

As an example, Casper described a famous trial which was frequently mentioned in legal medicine textbooks as a cautionary tale against trusting the senses in expert reports. By the end of 1851, a group of French doctors had to decide in court whether the blood found in the cellar of a woman accused of murder was human or, as she claimed, came from a sheep whose blood had been employed in domestic activities. The group included Barruel’s son and two well-known doctors: Jean-Baptiste-Alphonse Chevallier (1793-1879), who had collaborated with Barruel senior in many expert reports concerning bloodstains during the 1830s, and Ambroise Tardieu (1818-1879), who became the leading figure in French legal medicine during the second half of the nineteenth century. These experienced forensic physicians were unable to obtain any conclusive results by using Barruel’s test. Thinking that the cause was the presence of impurities, they decided to perform a blind trial with nine samples of blood obtained from different animals and humans, including the blood taken from the cellar. Each expert repeated the test for every sample, adding sulfuric acid to the blood and smelling the particular odor, and then wrote secretly in the laboratory notebook his view concerning the source of the blood for each sample.  While some of the experts guessed some samples correctly, others mistook in many cases the human blood for blood of other animals, and the other way round. Andrew Fleming, author of a pioneering book on bloodstains in legal medicine, described the episode in the following terms:

the disagreement between these experts was so great as to produce complete confusion in their own minds, and to destroy the confidence which had for a time been placed in this test. (Fleming 1861, 45). 

In a similar vein, caricaturized versions of this episode were included in many legal medicine textbooks as well as in popular narratives of bloodstain detection. The misleading situation was employed as a cautionary tale against the risks of following experts’ noses in both laboratories and courtrooms. In contrast, the previous analysis on the Barruel’s test shows that many nineteenth-century chemist and physicians, including influent forensic doctors, regarded the noses as “fine instruments of observation” which could detect minimal differences in the composition of blood, which neither microscopes nor spectroscopes could register at that time, like Friedrich Nietzsche remarked in the quotation at the beginning of this text. However, far from talking “in reverence and gratitude” about the virtues of their noses, many of them were acquainted of the difficulties to transform these smell nuances into convincing proofs in courtrooms. In fact, similar problems were faced regarding colors and microscopic images when detecting bloodstains in crime scenes. All these methods encountered challenges arising from the undisciplined conditions inherent in forensic investigations: scant quantities of blood, numerous sources of contamination, deceptive side-reactions, and, significantly, the rigorous standards of proof in murder trials. Criticisms of olfactory tests mirrored those concerns regarding the reliance on the sense of vision, particularly with respect to the identification of colors and deceptive optical illusions under microscopes. The disputes traversed from legal courts to medical academies, finding coverage in medical journals and popular newspapers. Participants in these debates comprised not only physicians, chemists, microscopists, and pharmacists but also lawyers, magistrates, and the general public. Divergent perspectives coexisted concerning the probative value of the sense of smell and its applicability across a broad range of scenarios in both scientific and criminal investigations.

Jose Ramon Bertomeu Sànchez
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