Digestion, ix, 226-46, x, 319-30, 353; benefited by savory food, ix, 98, 241-2; chemistry of, viii, 356-8; color effects, xi, 96; emotion effects on, ix, 165, 241; enzymes in, viii, 103, 357 (see Enzymes); excitement effects, xi, 374-5; exercise and, 339; fried foods and, ix, 286; fruit stimulation of, viii, 365; glucose in, 225-6; historical studies of, ix, 239-40, x, 121, 128; hot baths and, ix, 313; in men and plants, xiii, 109; of proteins, x, 204; sleep in relation to, ix, 219, xi, 285; soups as aid to, ix, 241, x, 320 (see also Indigestion) Digging with water jets, v, 88 Digitalis, source, xiii, 256; use of, in heart diseases, x, 333, 383 Dikes (geological), iii, 13, 110-11, 378, xiv, 106-8; columns in, 130; illustrations, iii, 102, 160 (Pl. 9); veins and, 383-4 Dilated Stomach, ix, 85 Dimension, illusions of, xi, 186, 188, 189; perception of, 162, 165, 171-2, 172-83 Dining rooms, lighting, vi, 275-6, vii, 69-70 Dinosaurs, iii, 288-93, 304 (Pl. 17), xii, 182, 194-5 Diœcious Plants, xiii, 47 Dionysus, worship of, xv, 352 Diophantus, xvi, 95 Dioptra, of Ctesibius, xvi, 91 Diphenyl, viii, 240 Dipper (constellation), moving clusters in, ii, 343 Diphtheria, x, 296-8; antitoxin of, 197, 212, 213-14, 218, 296-8; immunity to, 207, 298; named by Bretonneau, 110; toxin of, 196, 197 Direct Current Generators, iv, 307-8, vi, 159, 175-94, 344; commutators on, vii, 364-5; employment, vi, 215; voltages, 159 Direct Current Motors, vi, 217-39; in traction, vii, 182-3, 198-200; on farms, 224; speed flexibility, vi, 224-6, 229, 230, 232, 240-1 Direct Currents, vi, 152, 153-4, vii, 365; ammeters for, vii, 166-72; circuit-breakers for, 37, 39, 40; conversion from alternating, vi, 330-48; generation (See Direct Current Generators); inductance in, 166; lighting and magnetic effects, 155, 156-7; open-circuited by condensers, 170, 304; power consumed by, 165; transformers unusable, 309; transmission by, 160, 161, 195, 332; uses, 152, 332; used in electric furnaces, vii, 305-6; used in electrochemistry, vi, 163; used in electrotherapy, vii, 244; used in smoke precipitation, vi, 164; used in traction, 161-2, vii, 182, 186, 195; value of current flow, vi, 164-5 (see Ohm's Law); voltages, vii, 164; voltages, production of high, 349-50; voltmeters for, 154-65; wattmeters for, 172, 173, 175 Direct Lighting, xi, 277, 373 Direction, perception of, ix, 117-18, 120, xi, 165, 167-71 Directional Wireless, i, 291, 302 Dirigible Balloons, iv, 107-8, v, 226-30, 382; in forest service, i, 49 Disaccharides, viii, 224, 226-7, 375; enzyme of, 357 Discomfort, atmospheric, i, 318, 320, 322; senses of, in infants, ix, 351 Discordant Coasts, xiv, 249