The author examines premature and senescent changes as largely resulting from degeneration of internal-secretion (ductless) glands, particularly the thyroid, sexual glands, and adrenals, and treats old age as a chronic, treatable condition. He surveys experimental and clinical evidence and outlines hygienic and therapeutic measures to preserve vitality, strengthen glandular and circulatory function, and eliminate toxic products. Large sections address the cleansing roles and hygiene of the liver, kidneys, intestines, skin, and thyroid, and offer guidance on preventing arteriosclerosis, high blood pressure, and constipation. Practical chapters discuss heredity, diagnostics for estimating life-span, rational clothing, air baths, and cosmetic measures to mitigate aged appearance.