Classic description of the gross anatomy of the kidney. Bellini discovered the renal excretory ducts (“Bellini’s ducts”) and advanced a physical theory of the secretion of the urine. A translation of an extract from the 2nd ed. (1663) is in J. F. Fulton’s Selected readings in the history of physiology, 2nd ed., 1966, pp. 350-52.

Bellini began to develop his hydraulic iatromechanics in this work, in which he considered the blood as a physical fluid with simple mechanical and mathematicizable properties.  He realized the value of the urine as an aid to diagnosis and insisted on its chemical analysis in pathological conditions.