A colloidal suspension of various proteinaceous materials in water. Most familiar are those derived by boiling animal hides, tendons, or bones, which are high in collagen. Chief sources are slaughterhouse wastes and fish scraps. Other animal-derived glues are made from casein (milk) and blood. The most important vegetable glue is made from soybean protein. Combustible in solid form.See Adhesive; Fish Glue; Collagen; Gelatin.