Bacon's principal book was published in 1620, and called the "Novum Organum," or "the new instrument." It was obviously an invention, for it was a definite creation of a wholly new thing, that originated in a definite conception, and was developed into a concrete instrument. That Bacon so regarded it is evident from the title that he gave it. Furthermore, he described it as "the science of a better and more perfect use of reason in the investigation of things and of the true aids of the understanding." Bacon was a patient of Dr. Harvey, who discovered the circulation of the blood; and it would be strange indeed if Bacon's philosophy did not give to Harvey a great deal of guidance and suggestion that furthered his experiments. William Harvey discovered the fact that the blood circulates in the bodies of living animals. This declaration stated by itself would convey to the minds of some the idea that Harvey discovered it, somewhat as a boy might discover a penny lying on the ground. The first definition of the word discover in the _Standard Dictionary_ is "to get first sight or knowledge of"; so that the mere announcement that an investigator has "discovered" something gives to many people an incorrect idea of his achievement. Harvey discovered the fact of the circulation of the blood after years of experimentation and research on living animals, and by work of a most laborious kind. His conclusions were not accepted by many for a very considerable period; but he was fortunate, like Bacon, in holding a position of such influence and prestige, that he escaped most of the violent opposition that inventors usually meet. Harvey's discovery did not of itself constitute an invention; but the embodiment of that discovery in a concrete theory, so explained "that persons skilled in the art could make and use it," did constitute an invention of the most definite kind. The whole influence of that invention on history, only a highly equipped physician could describe; but, nevertheless, one may feel amply justified in stating that its influence on the science and practice of surgery and medicine, and on the resulting health of all the civilized nations of the world, has been so great as to be incalculable.