as evident in his earliest paper (1842) on the process of urinary secretion as in all his subsequent work. Ludwig exercised enormous influence on the progress of physiology, not only by the discoveries he made, but also by the new methods and apparatus he introduced to its service. Thus, in regard to secretion, he showed that secretory glands, such as the submaxillary, are more than mere filters, and that their secretory action is attended by chemical and thermal changes both in themselves and in the blood passing through them. Ludwig demonstrated the existence of a new class of secretory nerves that control this action, and by showing that if the nerves are appropriately stimulated the salivary glands continue to secrete, even though the animal be decapitated, he initiated the method of experimenting with excised organs. He devised the kymograph as a means of obtaining a written record of the variations in the pressure of the blood in the blood vessels; and this apparatus not only conducted him to many important conclusions respecting the mechanics of the circulation, but afforded the first instance of the use of the graphic method in physiological inquiries. For researches on blood gases, he designed the mercurial blood-pump that, with various modifications, has come into extensive use. He used it for many investigations into gases of the lymph, the gaseous interchanges in living muscle, the significance of oxidized material in the blood, etc. There is indeed scarcely any branch of physiology, except the physiology of the senses, to which Ludwig did not make important contributions. He was also a great power as a teacher and the founder of a school. Under him the Physiological Institute at Leipzig became an organized center of physiological research, whence issued a steady stream of original work; and though the papers containing the results usually bore the name of his pupils only, every investigation was inspired by him and carried out under his personal direction. Thus, his pupils gained a practical acquaintance with his methods and ways of thought, and, coming from all parts of Europe, they returned to their own countries to spread and extend his doctrines. Possessed himself of extraordinary manipulative skill, he abhorred rough and clumsy work, and he insisted that experiments on animals should be planned and prepared with the utmost care, not only to avoid the infliction of pain (which was also guarded against by the