The technical methods for microscopic examination given in Part II have been brought up to date, and all recent methods of value included. Original methods have been given in preference to modifications; the latter, when of value, are also mentioned. As a rule that method has been chosen which in the light of the writer’s laboratory experience has yielded uniformly the best results. An effort has been made to reduce the number of methods to the lowest number as representing the best and most indispensable ones. During the fourteen years of laboratory experience since the publication of the first edition there has been plenty of time for changes in points-of-view concerning laboratory methods. Then an ardent exponent of celloidin-imbedding as a routine method, the writer has now practically discarded it in favor of paraffin-imbedding and the celloidin-sheet made by the dextrin-sugar or molasses method. This combination method is so superior in every way to ordinary celloidin-imbedding that the latter becomes obsolete except for a limited number of conditions. A number of personal modifications of various methods will also be found in this part of the book; indeed, it is intended to be an expression of individual opinion concerning laboratory methods. The writer’s views concerning the value of teaching by _unknowns_,—that is, giving the student preparations or case-material for his own analysis and independent working-out to a diagnosis—are stronger now than they were when the preface to the first edition was written. Experiments with other methods of teaching have always brought me back to this as yielding by far the best results. It accomplishes two things—it not only teaches a knowledge of pathology, but it develops objectivity and the faculties of diagnosis, and accomplishes these with more marked success than any other method of teaching pathology. ALDRED SCOTT WARTHIN, Ph.D., M.D. ANN ARBOR, MICHIGAN, May, 1911. PREFACE TO THE FIRST EDITION. Pathologic Histology deals with departures from the normal in the various tissues of the body, which, occurring as the sequelæ of disease-processes, or standing in the closest causal relationship to the clinical symptoms and physical signs, constitute the foundation of all diagnostic conclusions, and of all rational therapeutic treatment. Without a definite knowledge of these abnormal changes, of their various forms, of the manner in which they arise and progress, no physician can deal intelligently with disease. The knowledge of the _natural history_ of disease, based upon a knowledge of the normal body, makes the wise and successful practitioner; and to such, the autopsy, the microtome and the microscope must ever stand as constant aids in the satisfying of his intellectual curiosity.