55. Knife for Bardeen freezing microtome 215 PART I. SOURCES OF PATHOLOGIC MATERIAL AND METHODS OF OBTAINING IT FOR EXAMINATION. INTRODUCTION. The chief sources of pathologic material are the autopsy, surgical operation, diagnostic excision and curetting, the spontaneous discharge of diseased tissue, and the experimental production of pathologic conditions in animals. To these sources may be added the blood and other body-fluids, as well as pathologic fluids, exudates, effusions, cyst-contents, etc., particularly the cellular elements found in the sediment of such fluids. That an accurate pathologic diagnosis be secured, the material must first be properly obtained, its gross characteristics carefully noted, the portion to be examined microscopically chosen with discrimination, and, finally, the microscopic examination itself carried out along the various lines indicated. All of these procedures require the knowledge of a certain amount of technique, and the general principles of such technique should be familiar to every student of medicine. While it is not possible that every medical graduate can enter into the active practice of his profession as an expert pathologist, yet the possession of the technical knowledge necessary to perform an autopsy properly and to select with discrimination the tissue for microscopic examination gives to a physician a distinct practical advantage. This advantage becomes the greater if to the possession of this knowledge there be added also a practical working knowledge of the technique necessary for the microscopic examination and diagnosis. Not that this knowledge should be so extensive as to cover the great field of special methods; all that is really essential is a knowledge of the general principles of laboratory examinations; and a very large proportion of practical work can be successfully carried out if the physician possesses this foundation knowledge. In the first days of practice a young physician so equipped often finds that his laboratory training comes to be his chief source of income and opens the way to a successful professional career. It constitutes a professional asset which the older practitioner usually does not possess. CHAPTER I. THE AUTOPSY: GENERAL CONSIDERATIONS.