Domenico Cotugno was a famous physician who lived in Naples in the 18th century. At the age of only 25 years, he published an important book on the anatomy of the inner ear that contained some theories concerning the physiology of hearing, the later developments of which were associated with the name of Hermann von Helmholtz. Three years later, he wrote a book on the physiopathological causes of sciatic pain, in which, for the first time in medical history, he differentiated true sciatic pain from the pain attributable to secondary causes. Using a series of meticulous dissections and elegant experiments, he showed that not only brain ventricles but also the subarachnoid spaces of the cranium and spine were filled with circulating fluid, which is why cerebrospinal fluid is also known as "liquor cotunnii."