Louis Tanquerel des Planches (1810-1862) only left us with one significant medical work, his Traité des maladies de plomb ou saturnines (treatise on lead or saturnine diseases), published in 1839. The work served as a reference for diagnosing and treating lead poisoning throughout the second half of the nineteenth century. The word “encephalopathy” that he coined at that time referred to toxic damage to the central nervous system. Whereas for two millennia and for most physicians, lead poisoning was considered lead colic, i.e. paroxysms of abdominal pain, Tanquerel collected seventy-two observations of damage to the central nervous system in workers exposed to lead in Parisian workshops (which no longer exist). He then inventoried and described forms of paralysis, delirium, coma, and convulsions related to lead poisoning. Having no qualms about stepping away from La Charité Hospital where he had treated patients with lead poisoning, he inspected their workplaces and unambiguously presented the deplorable conditions that caused so many patients to die. His “preservative” advice was an initial attempt at medical-social prophylaxis with the goal of helping the working class exposed in workshops without any respect for human life. With support from chemists and pharmacists, Tanquerel showed the presence of lead in brain tissue and thus demonstrated its neurological toxicity as early as 1839. This article is also an opportunity to note the contributions on this topic of some other physicians: François-de-Paule Combalusier (1713-1762), François Victor Mérat de Vaumartoise (1780-1851), Jean-Louis Brachet (1789-1858), Auguste Mirande (1802-1865), Vincent Nivet (1809-1893), Augustin Grisolle (1811-1869), and Ferdinand de Bernard de Montessus (1817-1899).