The bacteria discovered by Leeuwenhoek in 1687, 276. The development of the science of bacteriology of great importance to the human race, 276. Some general topics connected with the study of bacteria, 277. The spontaneous origin of life, 277-293. Biogenesis or abiogenesis, 277. Historical development of the question, 277. I. From Aristotle, 325 B.C., to Redi, 1668, 278. The spontaneous origin of living forms universally believed in, 278. Illustrations, 278. II. From Redi to Schwann, 278-284. Redi, in 1668, puts the question to experimental test and overthrows the belief in the spontaneous origin of forms visible to the unaided eye, 279. The problem narrowed to the origin of microscopic animalcula, 281. Needham and Buffon test the question by the use of tightly corked vials containing boiled organic solutions, 281. Microscopic life appears in their infusions, 282. Spallanzani, in 1775, uses hermetically sealed glass flasks and gets opposite results, 282. The discovery of oxygen raises another question: Does prolonged heat change its vitalizing properties? 284. Experiments of Schwann and Schulze, 1836-37, 284. The question of the spontaneous origin of microscopic life regarded as disproved, 286. III. Pouchet reopens the question in 1858, maintaining that he finds microscopic life produced in sterilized and hermetically sealed solutions, 286. The question put to rest by the brilliant researches of Pasteur and of Tyndall, 288, 289. Description of Tyndall's apparatus and his use of optically pure air, 290. Weismann's theoretical speculations regarding the origin of biophors, 292. The germ-theory of disease, 293-304. The idea of _contagium vivum_ revived in 1840, 293. Work of Bassi, 294. Demonstration, in 1877, of the actual connection between anthrax and splenic fever, 294. Veneration of Pasteur, 294. His personal qualities, 296. Filial devotion, 297. Steps in his intellectual development, 298. His investigation of diseases of wine (1868), 299. Of the silkworm plague (1865-68), 299. His studies on the cause and prevention of disease constitute his chief service to humanity, 299. Establishment of the Pasteur Institute in Paris, 299. Recent developments, 300. Robert Koch; his services in discovering many bacteria of disease, 300. Sir Joseph Lister and antiseptic surgery, 302. Bacteria in their relation to agriculture, soil inoculation, etc., 303. Knowledge of bacteria as related to the growth of general biology, 304. CHAPTER XIV Heredity and Germinal Continuity--Mendel. Galton. Weismann, 305