Provided herein are polymeric \u03b1-hydroxy aldehyde or \u03b1-hydroxy ketone reagents which can be conjugated to amine-containing compounds to form stable conjugates in a single-step reaction. The paper feed apparatus is provided with a guide distance adjustment device 14 for making a distance between the pair of guide members 12 and 13 variable. A deadening wall member extends along the first plane. The hook-retaining material may include a nonwoven material or a reticulated foam.