Bacteriology as a science is a development of the latter half of the nineteenth century. It may be said to have begun in the decade between 1870 and 1880, due largely to the wide circulation given to Koch’s work in proving that _Bacillus anthracis_ is the cause of Anthrax in 1876, in devising new culture methods and in demonstrating that wound infections are due to microörganisms, 1878. Associated with this work were the great improvements in the microscope by Abbé and the introduction of anilin dyes for staining bacteria by Weigert. These results attracted workers throughout the world to the “new science.” Nevertheless, this work of Koch’s was preceded by numerous observations and experiments which led up to it. Certainly the most important discoveries immediately responsible were those of Pasteur. He must be considered as the greatest of the pioneer bacteriologists since he worked in all fields of the subject. Some of the antecedent work was done in attempting to disprove the old “spontaneous generation” theory as to the origin of organisms; some in searching for the causes of disease and some in the study of fermentation and putrefaction. SPONTANEOUS GENERATION. Speculation as to the first origin of life is as old as history and doubtless older. Every people of antiquity had its own legends, as for example, the account in Genesis. This question never can be definitely settled, even though living matter should be made in the laboratory. The doctrine of the “spontaneous origin” of particular animals or plants from dead material under man’s own observation is a somewhat different proposition and may be subjected to experimental test. The old Greek philosophers believed it. Anaximander (B.C. 610-547) taught that some animals are derived from moisture. Even Aristotle (B.C. 384-322) said that “animals sometimes arise in soil, in plants, or in other animals,” _i.e._, spontaneously. It can be stated that this belief was general from his day down through the Dark and Middle Ages and later. Cardano (A.D. 1501-1576) wrote that water gives rise to fish and animals and is also the cause of fermentation. Van Helmont (1578-1644) gives directions for making artificial mice. Kircher (1602-1680) describes and figures animals _produced under his own eyes_ by water on plant stems. However, many thinkers of the seventeenth century doubted the truth of this long-established belief. Francesco Redi (1626-1698) made a number of experiments which tended to prove that maggots did not arise spontaneously in meat, as was generally believed, but developed only when flies had an opportunity to deposit their eggs on the meat. It seems that by the latter part of this century the idea that organisms large enough to be seen with the naked eye could originate spontaneously was generally abandoned by learned men.