PREFACE. THE following pages are intended to convey to the reader a concise account of the technical procedures necessary in the study of bacteriology, a brief descrip- tion of the life-history of the important pathogenic bacteria, and sufficient description of the pathological lesions accompanying the micro-organismal invasions to give an idea of the origin of symptoms and the causes of death. The work being upon Pathogenic Bacteria, it does not cover the whole scope of parasitology, and the parasites of higher orders are all omitted. Malaria and amebic dysentery are omitted as logically as tape-worms and pediculi. The higher fungi are also omitted, both because they are not bacteria and because their proper consideration would make a small book in itself. In leaving out the non-pathogenic bacteria of course a stumbling-block was encountered. The Sarcina ven- triculi, for instance, may be a cause of dyspepsia, yet "can scarcely be regarded as pathogenic, and, together with other similar bacteria of questionable deleterious operation, has been omitted; on the other hand, it has been thought advisable to include and describe somewhat -at length a long list of spirilla similar to, and probably closely allied with, the spirillum of cholera, yet not the cause of any particular diseased condition.