Habits, 354. Habitat of protozoa, 172. Habit formation, 354. Haemoglobin, 314, 330. Hammer, 359. Hard palate, 301. Harm done by insects, |34|, 225. Harmful green plants, 127; preservatives, 148. Hay infusion, 163, |164|. Head of a bee, |38|. Heart a force pump, |320|; diagram, |319|; in action, 319; internal structure, 319; of fish, 236; size, position, 318. Heat, and bacteria, 145; effect of, 22; output, 285. Heating the house, 375. Hemiptera, 32. Hen's egg, |246|. Herbivorous animals, 213. Heredity, and evolution, 404; bearers of, 251; definition, 249; relation of alcohol to, 372. Hervey, William, 399. Hibernate, 22. Hides, 205. Hilum, 59. Honey and wax, 207. Hookworm, 183, 228, |229|. Horse, ancestor of, |193|, |260|. How food is swallowed, 302. Human blood, |314|. Human body, a machine, 267; composition of, |21|. Human physiology, definition, 15. Humming bird, |43|. Humus, 79. Hundred calorie portions, |286|. Huxley, 398. Hybridizing, 254. Hybrids, 254. Hydra, |179|. Hydrochloric acid, 303. Hydrogen of water, |20|, 20. Hydrophobia, 392. Hygiene, 27; of breathing, 338; of skin, 344; of mouth, 302; of muscles and bones, 268; outline, 415; personal, 261. Hypocotyl, 59. Hymenoptera, 30. Ichneumon fly, |208|. Illness of drinkers, |363|. Imperfect flowers, 44, |45|. Immunity, 157, 390. Improvement, by selection, |253|; of man, 261. Impure water, 289. Incisors, |301|. Infectious diseases, 27, 363, 390. Infusoria, 182. Inner ear, 359. Inoculation, 157. Inorganic soil, |77|; foods, 274. Insects, 185; and foods, 376; as disease carriers, 225; as pollinating agents, 36; damage done by, |34|, 214; diagram of, |29|; food of, 33; of the house, 216; orders of, 30. Inspection, of factories, 379; of raw food, 380. Instincts, 195. Internal secretions, 317. Intestinal fluid, 306; glands, 308. Intestine, large, 309. Invertebrates, 185. Iris, 360. Isolation, 390. Jenner, Edward, |400|. Jimson weed, 128. Jukes, 261. Kidney bean, |59|, |63|. Kidneys, 181; human, |341|; of frog, 243. Kinetic energy, 267. Knots, 112. Koch, Robert, |403|.