"All natural bodies present themselves in a double relation, to wit: according as they are reckoned with apart and comprehended within the circuit of their own proper nature, or according as they are the instruments of some nobler and superior authority. For, as to their own proper powers, there is no doubt that all things which are subject to generation and corruption derive their origin from the elements, and work according to the standard thereof. In so far, however, as all things so subject are instruments of a more excellent agent and are regulated thereby, their works do not proceed from their own proper nature but from the rule of that other; and, consequently, they seem to be associated with another and more divine body and to exceed the powers of the elements."[354] In the very next Exercise, however, that On the Primitive Moisture, the last Exercise of Harvey's treatise On Generation, we come suddenly upon a reason why "the powers of the elements" must have seemed to him something to be treated rather as a convenient form of words than as a serious doctrine, despite his respectful argument just quoted. Speaking of the "primitive moisture," the great observer says that he sees in the hen's egg that out of that "crystalline colliquament," that "simplest body" alone, all the parts of the embryo are made and increased;[355] and proceeds bluntly to question the reality of the elements, "namely, the fire, air, water, and earth of Empedocles and Aristotle; or the salt, sulphur, and mercury of the chemists; or the atoms of Democritus."[356] Harvey says:-- "Therefore, the so-called elements do not exist prior to whatever is generated or arises; but rather are subsequent thereto, being remains rather than origins. Not even Aristotle himself, nor any one else, has ever demonstrated that elements exist separately in nature, or give rise to bodies which consist of parts similar one to another."[357] Almost immediately after this tug at the foundations of the Aristotelian universe, Harvey brings his treatise On Generation to an end.