'Eyw rpwvry ~OiWTO~ EV Tli E(}'rllup JOHN, J, 23 A SURVEY OF THE PRINCIPAL WORKS on histological technique that have th appeared since the end of the 19 century shows such a diversity of concept and directive ideas, in spite of the fundamental unity of subject, that the choice of the underlying orientation was perhaps the most difficult problem facing me when MM. Masson & Cie, requested me to write this book. A classification of these works based on their particular orientation and carrying the excess inherent in all that is schematic would lead to the definition of three types of books. Some are handbooks or treatises on microscopy . They are tacitly limited to the biological applications of the microscope, all of which are reviewed, and include in the same volume the techniques of histology proper along with those of bacteriology, botany and embryology. Such a work, on the scale of an encyclopaedic treatise contributed by specialists from a number of discip- lines and meant to be consulted as a dictionary, may have a certain value if it is really exhaustive and periodically revised. But it is longer possible on the scale of a handbook. A single person, however gifted, cant have acquired sufficient mastery over all the techniques of the above disciplines to be able to speak from personal experience.