We define B\"acklund--Darboux transformations in Sato's Grassmannian. They
can be regarded as Darboux transformations on maximal algebras of commuting
ordinary differential operators. We describe the action of these
transformations on related objects: wave functions, tau-functions and spectral
algebras.
This paper is the second of a series of papers (hep-th/9510211,
q-alg/9602011, q-alg/9602012) on the bispectral problem.Comment: 13 pages, LaTeX2e, uses amsfonts.sty and latexsym.sty, no figure
