In the short space of 160 pages the author of this monograph presents a fairly comprehensive review of present day conceptions regarding the water economy of the body under both physiologic and pathologic conditions. As indicated by the bibliography of 1,192 papers, the treatise is largely a review of known facts and theories, although some original data are presented. After a short discourse on the peculiar physical and chemical properties of water, which make it especially fit for its varied rôles in the living body, the author describes the various forms in which water occurs in the body. These he designates as follows: (1) that recognized as water of solution, (2) that loosely bound with colloids by a reversible reaction, (3) that which is chemically bound and (4) that which occurs in certain pathologic states, spoken of as free extra-cellular water. These forms are not clearly differentiated by the author.