The authors have correlated, in a concise form, much valuable information with regard to enzymes, and have indicated the original source from which more detailed knowledge may be obtained. Briefly, the arrangement is under the headings of properties of enzymes: introduction, enzymes in biologic processes, chemistry of enzymes and enzymatic reactions, and factors which influence enzymatic reactions; distribution of enzymes in the human and the animal body and in plants and micro-organisms; methods for the preparation and study—enzymes acting on fats and esters, carbohydrates, proteins and their derivatives, oxidases and oxido-reductases, zymases and catalase; practical applications of enzyme activity —uses in various industrial processes, laboratory reagents, therapeutic agents in clinical medicine and medical diagnosis. In a book relatively so comprehensive, it is surprising to note that there is no reference to the now rather widely used application of enzymes as a means of differentiation between the various organic silver preparations