This essay examines an early eighteenth-century Instrucció mèdica especulativa (Barcelona, 1706), one document in a collection of several dozen modern-era Catalan-language manuscripts housed in the library of the Hispanic Society of America (New York). This text is unique in the collection; the others are literary or musical texts, or monastery/clerical records. The Instrucció mèdica especulativa is an interesting example of a post-medieval practical medical guide, with specific diagnoses of a variety of ailments, and prescriptions to cure them. At the same time, the author bases the theoretical parts of his treatise on Galen and humoural theory. As a cultural artefact the Instrucció is a product of a turbulent time in and around Barcelona —the War of Spanish Succession— and Br. Josep's Capuchin monastery of Montcalvari (Sarrià) was destroyed in 1714, after which the brothers eventually settled in the new Convent of Santa Madrona on the Rambla dels Caputxins in Barcelona.