Dr. Lansing has attempted in this review to correlate the major part of the existing literature on the general physiology of aging. Studies on the permeability changes with age, the few existing viscosity studies, and other physical measurements are briefly evaluated. Considerable emphasis is placed on the inorganic chemical changes with age; a thorough discussion of this aspect of age changes is possible because of the volume of experiments that have been done. Some organic chemical changes are considered as well as the significance of age pigments, metabolic changes, and growth. Experimental studies bearing on the role of growth regulation in aging are also examined