French nineteenth-century toxicology was a science made for the prosecution in criminal poisoning cases – a science conceived for and mostly made in the Cour d’Assises. The main purpose of toxicologists was the detection of small quantities of poisons in corpses in order to provide unquestionable evidence in courts. This approach was based on high sensitivity tests based on qualitative analytical chemistry and proved to be very useful in many criminal cases. It faced the anxieties of the French notables and the main political and economic powers. However, this approach could hardly be employed in cases of industrial poisoning, where other forms of evidence were needed not only to detect but mostly to prevent poisoning in workers’ bodies. These dramatic health problems in the industry were largely neglected by toxicologists, judges and decision-markers during the nineteenth-century. The paper focusses on a particular case (the Pouchon affair, 1843-1844), which took place in a crucial period, either in the development of forensic medicine (new high sensitivity methods were introduced around 1840 and a controversy took place on their virtues and delusions) and occupational health (Tanquerel des Planches published his seminal book on lead poisoning in 1840). My paper is based on studies on history of toxic products connecting research on history of crime with recent works on history of occupational health, particularly the practices of agnotology and undone science related to the visibilization/invisibilization of toxic risks.

In the 1840s, the French chemist Auguste Laurent turned to the study of the “active principles” of alkaloids, which ranged from the medicinal properties of quinine and cinchonine, to the deadly poison of strychnine, to the intoxicating effects of morphine and nicotine. Laurent had recently returned from working with August Hofmann in Giessen, and soon after began using aniline to synthesize his own, artificial alkaloids. On hearing this, the physicist Jean-Baptiste Biot then approached him to compare the optical properties of his artificial alkaloids to the natural ones. Working with Biot and Apollinaire Bouchardat, the head pharmacist at the Hotel-Dieu, they found that while all the natural alkaloids deviated the plane of polarization of light, or were optically active, the artificial ones were not. Informed by earlier debates about the optical activity of sugar, and whether its conversion into alcohol was a chemical or biological process, they emphasized their results indicated a level of organization that went beyond chemical composition. This paper explores the way that Laurent, Biot and Bouchardat mobilized the concepts of activity and organization to explore the ability of plants to affect the body and maintain a distinction between natural and artificial compounds in the post-vitalist landscape. It also addresses the contextual factors suppressing these views in the chemical community, the use Pasteur made of them uniting his work on fermentation and crystallography, and his subsequent efforts to deemphasize his association with Laurent.

In the twentieth century, the proliferation of synthetic chemicals prompted US and European governments to introduce regulatory regimes for the control of chemicals. It was especially consumers’ concerns about artificial food additives and synthetic pesticides that inspired environmentalism and prompted a wave of environmental regulations in the postwar decades. However, aflatoxin, a mold-produced carcinogen, has challenged scientists’ and regulators’ notions of toxic substances and control ever since its discovery in 1960. This paper describes how scientists of the US Food and Drug Administration (FDA) and the Scientific Committee on Food of the European Commission studied this “naturally-occurring” toxic substance and developed regulatory strategies from 1960 to the early 1990s. The agencies quickly devised ways to classify and regulate aflatoxin within the legal frameworks for synthetic contaminants. In the early 1980s, Bruce Ames challenged the whole regulatory framework by arguing that the health effects of synthetic chemicals were insignificant compared to the ones of unavoidable natural toxins, such as aflatoxin. In the meantime, agricultural scientists had shown that the formation of aflatoxin depended as much on human agricultural practices as on environmental conditions. This paper analyzes when, how, and why Ames, Philippe Shubik, René Truhaut, and other key figures evoked aflatoxin’s naturalness. The paper argues that evoking the difference between synthetic and natural chemicals served the justification and legitimacy of regulations at specific points, rather than reflecting different ontologies or research practices in the study of toxic substances

The common tale about the “chemical revolution” in psychiatry is that it begins with the introduction of neuroleptics in the 1950s. The latter led, as most historians argue, to the dismantling of mental asylums: patients suffering from mental illnesses were increasingly treated as out-patients. This paper starts from a different standpoint. It discusses a series of works that were published in an era that predates the so-called “chemical revolution”: the first half of the twentieth century. The paper argues that the foundation of chemical interpretations of mental illness (and pharmacological treatment) was laid in the interwar period within clinical and experimental studies with mescaline. Research on the alkaloid mescaline, extracted from peyote and first synthesised in 1919, focused from the early twentieth century on possible analogies between mescaline intoxication and psychosis. This led to claims that biochemical or hormonal imbalances were the cause of mental illness (illustrated in particular with the example of schizophrenia and the so-called "m substance" in 1952). Focusing on published works by psychiatrists and neuroscientists (i.e. John Raymond Smythies, Humphrey Osmond, Roland Fischer, Kurt Beringer, Heinrich Klüver), the paper highlights the determinant role that biochemistry played for brain-centered explanations of mental illness, and conceptions of personality. It furthermore discusses how the senses (in particular eyesight) were examined in experiments to further the clinical association between mescaline intoxication and schizophrenia