on the circulation of the blood, and, lastly, the exhaustive work on respiration by Kegnauld and Reiset. Among Ludwig's personal friends, E. Du Bois-Reymond had between 1840 and 1850 constructed a theory of molecular physics of the nerve and muscle tissue, and Helmholtz, by means of wonderfully ingenious methods, had measured the rate of transmission of the stimulus in living nerves.
The road for physical investigations in physiology was, therefore, already open when Ludwig's book appeared. Moreover, the idea of a vital force, which on account of its obscurity had excited so much opposition, had now become meaningless for scientific investigation, and had besides received its deathblow through Lotze in 1842. What, however, was totally lacking before the appearance of Ludwig's book was a thorough introduction of physical reasoning and methods in physiological instruction. Anatomy was still the ruling branch of science even in physiology, and in some chapters of the latter the physiological problems were actually left out m favor of anatomical or comparative anatomical explanations. This was the more natural, because physiology was still taught by anatomists in most of the universities. Moreover, the regular course of instruction afforded the young physician abundant opportunity of acquiring a thorough anatomical education, while on the other hand a more rigorous training in physics was extremely difficult to obtain. Even to the present day this difficulty has never been satisfactorily overcome.
As anatomical demonstrator and professor, Ludwig himself had been through the dissecting room; he was all his life an excellent anatomist, and thought exceptionally highly of the mission of anatomy. However, in many ways his ideas of this mission differed from those of his predecessors, and even his language was often unlike what had hitherto been in use. He was especially energetic in opposing the idea that the mere description of forms could lead the way to a true understanding of physiology. The controversies between Ludwig and his opponents were vigorously carried on for several years, but at last they grew to understand one another better, and anatomists now have for years been accustomed to respect Ludwig as a valuable fellow-worker and one of the most eminent promoters of their science.
Perhaps nothing is more significant of Ludwig's point of view at the time of his first appearance than the arrangement of matter in his work on physiology. Ludwig's great predecessor, Johann Müller, had prefaced his manual of Physiology with a general chapter on organic matter, on organisms and life, and then proceeded to a description of the great vital functions: the formation and circulation of the blood, respiration, nutrition, etc. Ludwig, on the other
