The completion of the discovery of the circulation of the blood came in the person of Caesalpinus, who had received all of his education in Columbus' Century. Anyone who reads his description of the systemic circulation cannot fail to recognize that he really understood it. His discovery did not impress his generation as did that of Harvey in the next generation, nor did he understand so thoroughly the significance of his discovery. The Italians, however, have quite rightly insisted on vindicating for him the merit of having discovered the circulation of the blood, and some of them have even suggested that Harvey learned of it from him, but nothing can dim Harvey's glory as a great trained observer and original genius, who appreciated thoroughly the nature of the revolution that his discovery would work in the medical sciences. Harvey himself would have been the first to deprecate the lessening of the glory that was due to his predecessors or to his great teachers in Italy, one of whom, Fabricius da Aquapendente, belongs partly to our century. Indeed, in his book on the circulation, Harvey has given more credit to his predecessors than many of his ardent English advocates are prone to do in the modern time.
Professor Foster in his "Lectures on the History of Physiology During the Sixteenth, Seventeenth and Eighteenth Centuries," which were delivered as the Lane Lectures in San Francisco, and some of them also at Johns Hopkins, concedes Caesalpinus' priority of description. He says (page 33):
"He thus appears to have grasped the important truth, hidden, it would seem, from all before him, that the heart, at its systole, discharges its contents into the aorta (and pulmonary artery), and at its diastole receives blood from the vena cava (and pulmonary vein).
"Again in his 'Medical Questions,' he seems to have grasped the facts of the flow from the arteries to the veins, and of flow along the veins to the heart"
On page 35 of the same work Professor Foster says: "We must, therefore, admit that Caesalpinus had not only clearly grasped the pulmonary circulation, but had also laid hold of the systemic circulation; he recognized that the flow of blood to the tissues took place by the arteries and by the arteries alone, and that the return of the blood from the tissues took place by the veins and not by the arteries."
Foster is prone to make little of Caesalpinus as a man of book-learning rather than experimental or observational knowledge and as a scholarly writer rather than a scientific discoverer. It must not be forgotten, however, that Caesalpinus, besides being a great anatomist, is one of the most important contributors to the botany of this time. He was the director of the first botanical garden regularly established in Italy, that at Pisa, which still exists, and he is called by Linnaeus the first true systematic botanist. His work on plants distributed more than 1500 plants into fifteen classes distinguished by their fruits.
Every detail of the circulation is thus seen to have been understood, and Professor Foster has quoted the passages from Caesalpinus' books which make the necessity for such an admission very clear. The Italians have always claimed the discovery of the circulation for Caesalpinus, and the Southern nations of Europe generally have been inclined to favor that claim, though the Germans and English have refused to admit that even Caesalpinus' description, with all its clearness of detail, can be taken to mean that he understood the new doctrine that he thus was teaching. Besides, it is pointed out that Caesalpinus' new doctrines met with very little response and indeed scarcely any notice from his contemporaries. It must not be forgotten, however, that Harvey himself hesitated for some dozen years to publish his demonstration of the circulation of the blood, and there is good reason to believe that while he presented his views to his class in 1616 and wrote his treatise in 1619, he delayed its publication until 1628 and was even then apprehensive lest its appearance make "mankind his enemy." It is not surprising, then, in the light of this recognized attitude of the scientific mind of the time that Caesalpinus' declarations of half a century before should have been passed [{374}] over by scientists without proper recognition of their significance.
Any account of the development of the biological sciences at this time would be quite incomplete without the great story of the botanists who laid the broad, deep foundation of their favorite science during this century. The first distinguished name among them is that of Leonardo da Vinci, the story of whose work in botany seems almost incredible until the actual notes of his observations are before one. While Leonardo has been thought of always as a painter and only recently has the idea of his greatness as a scientist become generally known, he deserves eminently to be classed as one of the greatest of scientific geniuses. It was in the biological sciences that he did his most wonderful work. He knew the anatomy of men and animals very well and studied whole series of questions touching living beings. He did work in botany, palaeontology, zoology, physiology, so that Duval did not hesitate to speak of him in the Revue Scientifique [Footnote 33] as A Biologist of the Fifteenth Century. He made special observations on flying, on swimming, on the saving of life in shipwreck, on the mechanics of joints, on horse movement, so that he anticipated what we have learned by the camera. His special contribution to physiology was that certain acts of the nervous system are reflex, that is, without requiring attention from the higher centres.
[Footnote 33: December 7, 1889.]
His studies in color are among the most interesting done up to his time. These were not merely taken up from the physical standpoint but especially from the physiological, and his theory of color vision still attracts attention. He studied sound and made many valuable observations once more physiological as well as physical. His most interesting scientific conclusion was doubtless that with regard to fossils. Having met with them deep below the surface of the earth, he declared that they were not there by accident nor by any incompleteness of creation, but that they represented living things which had been covered up. He even suggested that marine fossils pointed to the fact that the sea had at some time covered this spot where [{375}] the fossils were found, though this was now far from water and well above its level.