The writing of a preface is perhaps superfluous for a book which has had a large and steady sale for nearly twenty years, and which has evidently met with the approval of a large constituency. A few words of introduction appear, however, desirable in view of the facts that the present edition has been almost entirely re-written; that a large amount of new matter has been introduced; and that, so far as is known, the comments on each subject represent the most recent and authoritative knowledge upon it.

An attempt has been made to meet the requirements of medical students, as well as of science students and general readers, for whom former editions were chiefly intended. A large class of medical students and practitioners do not require the detailed statement of the subject contained in the larger text-books. For them, and, it is hoped, also for a large number of candidates for diplomas in public health and in sanitary science, the present edition will prove to be useful. At the same time, the subject has been treated as non-technically as is consistent with accuracy, in order to retain its suitability for non-medical readers. A large number of new illustrations have been introduced.

The new chapters dealing with Dietetics, Trade Nuisances, Meteorological Observations, Tuberculosis, Disinfection, and Vital Statistics will, it is believed, enhance the value of the book.

Attention is also drawn to the solutions of mathematical problems in the different branches of hygiene, of which a table of contents is given on page viii.