Although Josef Breuer is probably best known for his work with Sigmund Freud on hysteria, he spent the most productive part of his scientific career working on the vestibular receptors of the inner ear. With the physicist Ernst Mach, he developed the Mach-Breuer theory of semicircular canal function. He was the first to recognize that nystagmus resulted from endolymph flow within the semicircular canals and that the ampullary nerve of a single canal could sense endolymph flow in both directions. By carefully studying the anatomy of the macules of fish, reptiles, and birds, he concluded that linear head displacements or tilts cause the otolithic membrane to slip, bending the hairs that project into it and thereby stimulating the underlying sensory receptors. His "shear theory" of hair-cell stimulation is a standard in modern textbooks of vestibular physiology. Breuer was truly a renaissance man who was as comfortable discussing philosophy and literature as he was the natural sciences.
Wiest G, Baloh RW. The Pioneering Work of Josef Breuer on the Vestibular System. Arch Neurol. 2002;59(10):1647-1653. doi:10.1001/archneur.59.10.1647