 These and similar considerations led Aristotle to question whether the atomists had a concept of substance at all. There are a large variety of substances discernible in the world—the flesh, blood and bone of animal bodies; the water, rock, sand and vegetable matter by the coast, etc. Atomism apparently makes no provision for accommodating the differing properties of these substances, and their interchangeability, when for example white solid salt and tasteless liquid water are mixed to form brine or bronze statues slowly become green. Aristotle recognized the need to accommodate the creation of new substances with the destruction of old by combination involving the mutual interaction and consequent modification of the primary features of bodies brought into contact. In spite of the weaknesses of his own theory, he displays a grasp of the issue entirely lacking on the part of the atomists. His conception of elements as being few in number and of such a character that all the other substances are compounds derived from them by combination and reducible to them by analysis provided the seeds of chemical theory. Ancient atomism provided none.