Ventilation, importance of, 7; motion, coolness, humidity, and freshness, of air chief features of, 7; overemphasis of danger from drafts, 8-9; by means of windows, 9; use of window-boards, 9-10; air-fans as a help in, 10; heating systems and, 10-11; importance of cool air and enervating effect of hot, 10-11; dryness and humidity of air, 11-12; relation of clothing to, 14-18; necessitated by conditions of civilization, 147; as a preventive of colds, 275. Vermin, diseases spread by, 74-75. Vertigo, causes of, 123. Vital resistance, increased by outdoor sleeping, 21-22. Vital surplus, conservation of, 5. Vitamins in foods, 42; importance of well-being of body, 42. Walking, correct posture in, 58-59; as exercise, 94; pleasures of, as recreation, 99; for overweight, 217. Water, drinking, with meals, 48; varying effects of habits of drinking, on constipation, 52; freeing from typhoid germs, 72; importance of pure supply of, 162. Water closets, height of seats of, 54. Weak feet, causes of, 60; disturbances of health due to, 224; means of detecting, 224-225. Weight, relation of, to longevity, 30-32; the correct average, 213-214; standards for, at various ages and heights, 214; avoidance of sudden reduction in, 217-218. _See_ Overweight _and_ Underweight. Wheat-bran, a preventive of constipation, 52. Whisky, not to be taken for colds, 280. _See_ Alcohol. Wholesale costs of uncooked ingredients of standard foods, 192-193. Will, exercise of the, 97-98; effort of, necessary to hygienic living, 126-127. Window-boards, use of, 9-10. Windows, best ventilation to be had through, 9. Wood fires as ventilators, 10. Woody fiber necessary in diet, 41. Wool, use of, in clothing, 17. Work, normal, one of the great blessings of life, 91; arrangement of hours for, 92; need of variety of, 92. _See_ Labor. Work and play, the two great forms of activity, 89; adjusting the proportion of, 90. Working conditions, disadvantages of the poor regarding, 128-129. Worry, physical sources of, 105-106; physical effects of, 112; practising art of serenity as an offset to, 113; ailments aggravated by, 123. Writer's cramp, cause of, 62. Yard-arm exercise for faulty posture, 221-222. Yellow fever, carried by mosquitoes, 71. Zhebrovski, E. A., experiments of, with cigaret-smoking rabbits, 255.