In presenting the subject of Bacteria, I wish to disclaim any originality for the matter offered. I have endeavored to collect from such sources of information as I have access to the important dates, names and facts which have marked the progress of bacteriology up to the present time. So far as we know, the first observer of bacteria and the so-called infusoria was Leeuwenhoek, who, with a simple magnifying glass, noticed in a drop of putrid water the multitude of little granules moving about in it. This was in 1675, and his observations were communicated to the Royal Society of Sciences in the same year. In the following year he recognized bacteria in the tartar from the teeth, and though he did not name them, his description of their forms and his drawings enable us to identify them as vibrios. There appears to have been no important investigations carried on until nearly one hundred years later, or in 1773, when Müller, a Dane, attempted to classify the organisms then known. He called them all infusoria, from the fact that they were the product of infusions, and divided them into two genera—the monas and vibrio. The monas he subdivided into ten forms and the vibrio into thirty-five; but his descriptions of them are so faulty that it is at present impossible to identify them from his writings. During the following century the study of bacteriology attracted more or less attention, and in 1829 Eherenberg, who is the Humboldt of the science, commenced his investigations, which for fifty years he pursued with an ardor and enthusiasm second to not even Darwin himself. He, in 1838, classified the family of vibrioniens, and with the additions made by Dujardin in 1841, placed them in a scientific category. Of course during this period many were the disputes and discussions as to specie, genera or family, each newly discovered member belonged to. And we have to come to the period of Hallier, Hoffmann and Cohn, and many others, before the questions, which had up to that time been in dispute, were settled. Ehrenberg’s original classification was into: 1. Bacterium, or rod-like—three species. 2. Vibrio, snake-like and flexible—nine species. 3. Spirillum, or spiral, but inflexible—three species. 4. Spirochœte, spiral, but flexible—one species. Dujardin, in 1841, in his Natural History of the Zoophytes, accepted the classification of Eherenberg, except that he unites the spirillum and spirochœte, calling them all spirillum. Up to this time all bacteria had been considered animals, but a close study of their life history and habitat by those who followed declared them to belong to the vegetable kingdom, and as such they are accepted to-day.