Geology became a science in Germany through A. G. Werner, in Freiberg, at the be ginning of the century, and L. v. Buch devel oped the doctrine of the slow upheaval of con tinents; his geological map of Germany ap peared in 1824. But greater was their pupil, Alexander von Humboldt (1769-1859), the most comprehensive German naturalist of his time. His studies in South and Central America and in Asia, his incomparable richness of observa tion in all fields of descriptive science, his unifying apperception of nature, as expressed in his (Kosmos,) make him the most imposing and most sympathetic figure in the German science of the first half of the last century.
Inasmuch as Humboldt's geography was es sentially physical, it seemed opposed to the historical-geographical interest. A synthesis of both tendencies characterizes the work of Carl Ritter (1779-1859), whom his time considered the founder of scientific geography. His con tributions to theoretical geography found a bril liant continuation through Peschel, Kiepert, Ger land, Ratzel, and others. In the meantime, prac tical geography was stimulated by Richthof en, Peschuel-Losche, etc. Well known are the maps of Petermann, Perthes, etc.
Geography may connect the inorganic with the organic world. To begin with botany, the first decades of the last century belonged to plant anatomy; the highest point was reached by H. v. Mohl. Then came, about 1840, the turn to the genetic study and the development of plant histology. The epoch-making discov eries of Schleiden (1804-81) and of Nageli showed the way. The morphologic work, partly with histological, partly with phylogen etic interest, was continued by Schwann, Hof meister, Pringsheim, DeBary, Strasburger, Solms, etc. The fundaments of plant physiology were laid by. Julius Sachs, whose 'Experimental Physiology of Plants> appeared in 1865. Pfef fer, Klebs, Stahl, etc., followed.
In zoology the century began with systematic interests, but turned soon to morphological ones and came on this path to the brilliant achieve ments connected with the names of Kollicker and Siebold, Ehrenberg and Max Schultze, Ley dig, Leuckart, and Hertwig. The leader in com parative anatomy, which started in Germany with Meckel, the UGerman Cuvier,l' was Gegen baur ; the prophet of Darwinism became Hxckel, and the most influential critics of Darwinism, Wagner and Weismann.
The progress of human anatomy links itself partly with the same names which became in fluential in zoology; at the middle of the cen tury the anatomists Henle, Hyrti, Baer, and Kallicker stand as the acknowledged leaders. His, Hertwig, Roux, and Waldeyer represent the later decades. Yet, it is characteristic for the German mind, that its most brilliant achieve ments belonged to physiology rather than to anatomy. No field, indeed, has greater names than physiology, with Joh. v. Muller and Helm holtz. lludolphi and Burdach, whose large physiology appeared in 1832, made physiology at home in Germany, and soon came the master, Johannes v. Muller (1801-58). His influence— it is said that he wrote 16,000 printed pages was deeply felt throughout physiology, embryol ogy, anatomy, and zoology; most popular is, per haps, his doctrine of the specific energy of the senses. Among his many important pupils none was greater than H. v. Helmholtz (1821-94), whose invention of the ophthalmoscope (1851) created the new ophthalmology. His physio logical optics and his book on tone sensations are still authoritative to-day. Dubois-Rey mond's investigations of electrophysiological phenomena, and Ludwig's analysis of the func tions of the heart opened new ways also, and so did Voit, Pettenkofer, Hering, Briicke, Pfliiger, etc., in various directions.
In the development of pathology the central figure is Rudolf Virchow (1821-1902), whose cellular pathology revolutionized the theory of disease and led it to the heights of modern histology. His pupils, Cohnheim and Reck linghausen, continued his proof that the organic laws working in disease are identical with those of the normal organism. A new movement came in with bacteriology; the discovery of the tubercle bacillus (1882) through R. Koch and his investigations of anthrax, turned his atten tion from the diseased cell to the microscopical causes of the diseases. From bacteriology pa thology finally turned to chemistry, studying the substances produced by the diseased tissues. This led to the theory of antitoxins and to Behring's discovery of the antitoxin treatment of diphtheria. Practical medicine was in the meantime led by men like Frerichs and Erb, Langenbeck and Billroth, Graefe and Griesinger.