On Urines

This chapter concentrates on John’s uroscopic theories as presented in his On Urines. It starts by examining the structure of the work, showing John’s intention to systematize knowledge on the subject by dividing his treatise into four large thematic areas, i.e. introductory details, diagnosis, aetiology, and prognosis, thus presenting a general-to-specific approach in each section. The analysis then shifts to John’s theories on the various stages of human digestion, which had remained undisputed for centuries. It is shown that John is eager to present his own understanding, especially on the role of the liver. John’s own observations are also evident in his discussion of the different colours of urine thanks to the extra explanatory information he provides in this respect, especially on how to differentiate between various colours. The last section focuses on John’s urine vial, which although identified as an important feature of his original approach by earlier scholars, was never fully contextualized in light of a holistic reading of John’s work or of the development of other, non-Byzantine, medieval theories on the subject. Consequently, it is argued that John’s most original contribution is the introduction and detailed definition of eleven subdivisions in the urine vial compared to the three areas traditionally identified.