Unifying power of the cell-theory, 237. Vague foreshadowings, 237. The first pictures of cells from Robert Hooke's Micrographia, 238. Cells as depicted by Malpighi, Grew, and Leeuwenhoek, 239, 240. Wolff on cellular structure, 240, 241. Oken, 241. The announcement of the cell-theory in 1838-39, 242. Schleiden and Schwann co-founders, 243. Schleiden's work, 243. His acquaintance with Schwann, 243. Schwann's personal appearance, 244. Influenced by Johannes Müller, 245. The cell-theory his most important work, 246. Schleiden, his temperament and disposition, 247. Schleiden's contribution to the cell-theory, 247. Errors in his observations and conclusions, 248. Schwann's treatise, 248. Purpose of his researches, 249. Quotations from his microscopical researches, 249. Schwann's part in establishing the cell-theory more important than that of Schleiden, 250. Modification of the cell-theory, 250. Necessity of modifications, 250. The discovery of protoplasm, and its effect on the cell-theory, 250. The cell-theory becomes harmonized with the protoplasm doctrine of Max Schultze, 251. Further modifications of the cell-theory, 252. Origin of cells in tissues, 252. Structure of the nucleus, 253. Chromosomes, 254. Centrosome, 256. The principles of heredity as related to cellular studies, 257. Verworn's definition, 258. Vast importance of the cell-theory in advancing biology, 258. CHAPTER XII Protoplasm the Physical Basis of Life, 259 Great influence of the protoplasm doctrine on biological progress, 259. Protoplasm, 259. Its properties as discovered by examination of the amoeba, 260. Microscopic examination of a transparent leaf, 261. Unceasing activity of its protoplasm, 261. The wonderful energies of protoplasm, 261. Quotation from Huxley, 262. The discovery of protoplasm and the essential steps in recognizing the part it plays in living beings, 262-275. Dujardin, 262. His personality, 263. Education, 263. His contributions to science, 264. His discovery of "sarcode" in the simplest animals, in 1835, 266. Purkinje, in 1840, uses the term protoplasma, 267. Von Mohl, in 1846, brings the designation protoplasm into general use, 268. Cohn, in 1850, maintains the identity of sarcode and protoplasm, 270. Work of De Bary and Virchow, 272. Max Schultze, in 1861, shows that there is a broad likeness between the protoplasm of animals and plants, and establishes the protoplasm doctrine. The university life of Schultze. His love of music and science. Founds a famous biological periodical, 272-274. The period from 1840 to 1860 an important one for biology, 274. CHAPTER XIII The Work of Pasteur, Koch, and Others, 276