text: The intrinsic viscosity is very sensitive to the axial ratio of spheroids, especially of prolate spheroids.  For example, the intrinsic viscosity can provide rough estimates of the number of subunits in a protein fiber composed of a helical array of proteins such as tubulin.  More generally, intrinsic viscosity can be used to assay quaternary structure.  In polymer chemistry intrinsic viscosity is related to molar mass through the Mark–Houwink equation. A practical method for the determination of intrinsic viscosity is with a Ubbelohde viscometer.