Material anatomical entity, each instance of which is either in fluid or solid state, with or without admixture of some cells and biological macromolecules; produced by some anatomical structures or derived from some inhaled or ingested substances that have been modified by anatomical structures. Examples: portion of saliva, portion of semen, portion of cerebrospinal fluid, portion of respiratory air, portion of urine, feces, portion of blood, portion of plasma, portion of lymph.