Desirable matrix materials for reagent layers are non-fibrous and can include non-interfering hydrophilic materials including acid-hydrolyzed gelatins, e.g., pigskin gelatins, or derivatives thereof having an isoelectric point of about 9.1, hydrophilic cellulose derivatives, polysaccharides such as dextran, gum arabic, agarose and the like, and also synthetic substances such as water-soluble polyv