Natural polymers include for example proteins such as glue, gelatin, albumin and casein; natural rubbers such as gum arabic and tragacanth gum; glucosides such as saponin; alginic acid and derivatives thereof such as propylene glycol alginate, triethanol amine alginate and ammonium alginate; and cellulose derivatives such as methyl cellulose, carboxymethyl cellulose, hydroxymethyl cellulose and et