Excerpt from Pathogenic A Text-Book of Microbiology for Physicians and Students of Medicine This volume is the outgrowth of an attempt to revise the well-known Williams Manual of Bacteriology, undertaken at the invitation of the Publishers, Messrs. P. Blakiston's Son and Co., very cordially seconded by Dr. Williams, who kindly placed the material of the previous editions at my disposal. The text has been very largely rewritten and the order of treatment considerably altered. Many of the illustrations of Dr. Williams have been retained and, as they have not been acknowledged in the legends, I wish to express my special obligation for them in this place. The book is intended as an introduction to the study of pathogenic micro-organisms and is designed especially for the use of physicians and students of medicine. During the past decade, the parasitic protozoa have assumed an importance which places them almost on a par with the bacteria as pathogenic agents, and the extension of bacteriological methods to the study of molds, yeasts, filterable viruses and protozoa has tended again to reunite the various portions of this field of knowledge, much as it was in the days of Pasteur. The attempt has here been made to outline the subject and to present a few examples under each important heading, in the hope that the student may become acquainted with the broad principles of the science and appreciate the variety of procedures, conceptions and organisms with which it deals. Part I is devoted to a description of technical procedures, Part II to the general biology of micro-organisms and Part III to a consideration of individual microbes. Much has of necessity been omitted and many topics treated only very briefly.