Guard ceUs, 24, 141, 143 



Guinea pigs, 107; scurvy in, 106; pigmen- 

 tation in, 479 



GuUet, 166 



Gums, 216 



Gymnosperms (jim'no spurmz), frontispiece, 

 691 



Gypsy moth, 353, 594, 596 



Haber, Fritz (1868-1936), 153 f. 



Habits, 318 



Hair, color of, 63 ; follicle of, 217 



Hales, Stephen (1677-1761), 146 



Hand, human, 50 



Haploid (hap'loid) number, 386, 403 



Happiness, 658 ff. 



Harvey, WiUiam (1578-1657), 185 



Hatchery, 380 



Hatching of insects, 352 



Hay fever, 371 



Hazards, occupational, 636 f. 



Head, of mammals, 14; of insects, 14 



HeaUng, 228 ff. 



Health, and sickness, 326 ; and mind, 330 flf. ; 



differences in, among cities, 607 ; and 



social status, 607 ff. 

 Hearing, 286 f. 

 Heart, 189 ff. ; muscular action of, 124 ; and 



carbon dioxide, 302 

 Heat, radiation of, from body, 116 

 Heidelberg man, 52 

 Height, variation in, 69, 70 

 Hehum (he'll iim), 84 

 Hemocyanin (he mo si'c nin), 102, 207 

 Hemoglobin (he mo glo'bin), 189, 205 f. ; de- 

 fective content of, 100 ; iron in, 102 

 Hens, egg production by, 649 

 Hepaticae (he pat'i se), 689 

 Herbivores (hur'bi vorz), 150, 151 ; teeth of, 



176 

 Heredity, 472 ff . ; in plants, 480 ; in animals, 



481 ; and reproduction, 483 ff. ; in man, 



500 

 HereUe, Felix d' (1873- ), 445 

 Hermaphrodite (her maf'ro dit), 386 

 Hertwig, Oskar (1849-1922), 376 

 Hessian fly, 594, 655 

 Hibernation (hi ber na'shim), 177 

 Hilum (hl'lum), 415 

 Hippocrates (430-370 B.C.), 103, 301 

 Homeostasis, 193 



Homologies, 458 ; invertebrate, 49 



"Homunculus", 347 



Hoof-and-mouth disease, 445 



Hooke, Robert (1635-1703), 21, 22 



Hookworm, 177, 244, 615, 616 



Hopkins, Frederick G. (1861- ), 107 



Hormones (hor'monz), 303 ff. ; plant, 258 

 ductless glands and, 306 f . ; and release 

 of energy, 312 f. ; and emergencies, 313 

 as unifiers, 315 ; and emotions, 315 ff. 



Horse, appendix of, 175; teeth of, 176 

 fossils of, 453 



Host of parasite, 177 



Human body, 13 f. ; composition of, 97 



Humming-bird, 176 



Humors, 301, 304 



Hunger, 195 



Hybrid corn, 498, 499 



Hybrids (hi'bridz), 474, 475 ff. ; human, 518 



Hydra (hi'dra), specialization in, 274, 382, 

 384 



Hydrogen, in protein, 97 



Hydrophobia, 614 



Hyphae (hi'fe), 375, 689 



Hypocotyl (hi p6 kot'il), 415 



Hypophysis (hi pof'i sis), 305, 306 



Ignorance and sickness, 608 f . 



Illness, causes of, 335 



Illumination and growth, 252 ff. 



Imagining, 57 



Imitation by animals, 56 



Immunity, 63, 234 ff. ; in plants, 244; 



natural, 244 ; breeding for, 496 

 Inbreeding, 476 

 Incisors, 176 

 Individuals, differences between, 61 ff., 



71 ff. ; uniqueness of, 66; and equalitv, 



71 f. 

 Indole-acetic acid, 258 

 Industries, hazards in, 637 f. 

 Infancy, among animals, 420 ff. ; in man, 



354, 426 f. 

 Infant death rates, 545, 547, 606, 610 

 Infantile paralysis, 294, 445 

 Infection, chain of, 618 

 Influenza, 445 

 Infusoria, 692 

 Inheritance, 472 ff. ; and chromosomes. 



486 ff. ; of differences, 507 f . 

 Inoculation, 235 



711 



