(1) Prof. Marshall's volume is a text-book of general and applied microbiology. The morphology, cultivation, and physiology of micro-organisms are first dealt with, and an excellent account of these subjects is given. If any chapter were to be selected for special commendation, we should choose Chapter II., partly perhaps, because of its novelty in a work of this kind, in which the physical forces involved in biological activities are described. An admirable summary is here given of such subjects as ionisation and dissociation, surface tension, adsorption, diffusion, and osmosis, colloids, and crystalloids—all of which are of fundamental importance for the understanding of biological activity. The second half of the book is devoted to applied microbiology, and accounts are given of micro-organisms in relation to air, water and soil, milk and foods, fermentations and disease, including the microbial diseases of plants and insects as well as those of man and animals. Twenty-five specialists in their various subjects contribute to the making of the book, and Prof. Marshall has edited and coordinated the whole. We know of no other book which in so limited a space gives such an excellent account, general and special, of micro-organisms in all their aspects. The text contains numerous illustrations. (1) Microbiology. Edited by Prof. C. E. Marshall. Third edition revised and enlarged. Pp. xxviii + 1043 + 1 plate. (London: J. and A. Churchill, 1921.) 21s. net. (2) Laboratory Manual in General Microbiology. Prepared by the Laboratory of Bacteriology and Hygiene, Michigan Agricultural College. Second edition. Pp. xxii + 472 + 1 chart. (New York: J. Wiley and Sons, Inc.; London: Chapman and Hall, Ltd., 1921.) 21s. net. (3) Die Anaphylaxie. By Prof. Ch. Richet. Autorisierte Ubersetzung von Dr. med. J. Negrin y Lopez. Pp. iv + 221. (Leipzig: Akademische Verlagsgesellschaft m.b.H., 1920.) n.p. (4) A Treatise on the Transformation of the Intestinal Flora, with Special Reference to the Implantation of Bacillus Acidophilus. By Prof. L. F. Rettger H. A. Cheplin. Pp. vii + 135 + viii plates. (New Haven: Yale University Press; London: Oxford University Press, 1921.) 12s. 6d. net. (5) Diagnosis of Protozoa and Worms Parasitic in Man. By Prof. R. W. Hegner Prof. W. W. Cort. Pp. 72. (Baltimore, Maryland: The Johns Hopkins University, School of Hygiene and Public Health, 1921.) n.p.