Abstract
A coronavirus isolated in tracheal organ cultures from the faeces of a calf with diarrhoaea readily multiplied on passage in intestinal organ cultures. Evidence for multiplication was obtained by the production of viral haemagglutinin in organ culture fluids and the presence of immunofluorescence and viral particles in the columnar epithelial cells of the villi. Thus virus multiplication was studied in vitro in the cell type in which it multiplies naturally.