This theory, which to-day appears so natural that we conceive with difficulty why it was not sooner discovered, was nothing less than a revolution in physiology; it excited a tremendous controversy that continued more than twenty-five years, and in which mingled every one possessed of any pretension to knowledge of anatomy or physiology; even naturalists and philosophers took part in the dispute. René Descartes was the first to declare in its favor and to support it by experiment; John Walæus (Jan de Wale), the celebrated Professor of Anatomy in the University of Leyden, confirmed it by new observations; finally Plempius, of Louvain, for a time one of the most fiery of opponents, succumbed to the truth, and in 1652 passed publicly to the ranks of Harvey's followers--no small triumph! During these long debates Harvey remained always dignified and firm, although the early attacks rendered him unduly sensitive regarding others which he anticipated. About{158} his only answer to the arguments adduced against him, was to add new proofs and new experiments to those already published. The only one of his adversaries who obtained a direct response was Riolan, who possessed immense influence among his contemporaries as a man of attainments; Riolan combated with equal violence and obstinacy the other great discovery of the age,--viz., the circulation of the lymph. Harvey ultimately, however, had the satisfaction of seeing his theory universally adopted. But his services were not limited to this one discovery. He made most interesting observations on generation, both in man and in animals; on midwifery; and on the structure and diseases of the uterus. The intermediary system and bond of union between the arteries and veins, so very essential, yet up to this time unknown, was discovered by the great Malpighi, who was born in 1628 near Bologna, became professor in its university, and discovered in the lungs and mesentery of frogs, in 1661, the capillary circulation. He first described the corpuscles of the blood in 1665; he also discovered the lung-cells, as well as the cutaneous glands, certain portions of the kidney, and the pigmentary layer of the skin, named after him (_rete Malpighi_), which later furnished the first explanation of the difference of color in different races.