Koch, on microbe of tuberculosis, 212 Lactic acid, arrests putrefaction, 255 Lady-birds and nectar, 32 Language, as a social band, 297 Lankester, Ray, on centenarians, 259 Lanugo, of human embryo, 62 Larvæ, of ephemerids, 276 Lecky, on natural morality, 8 Lejoncourt, on centenarians, 280 Leucocytes and phagocytes, 240 Liberty, future limitation of, 301 Life, duration of, in Biblical times, 259, 260 modes of lengthening, 257, 258 Light, attractive to insects, 35 Linnæus, on origin of man, 41 Lister, and antisepsis, 209 _Listera ovata_, figure of, 32 Loeb, on natural death, 266 Longet, on old age, 234 Longevity, in birds, 232 and large intestine, 252 in Old Testament, 259, 260 Love, Guyau on, 196 spreading of, 295 Lubbock, on ancestor-worship, 150 an optimist, 117 Luminous insects, 37 Luther, Martin, on supernatural origin of disease, 164 Luxury, evils of, 293, 294, 301 Macrophags, definition of, 240 functions of, 240 in senile decay, 241 Maeterlinck, on pessimism, 191 Mailaender, on pessimism, 187, 188 Malignant tumours, science and, 214 Mammary glands, rudimentary, 298 Man, destiny of, 286 disharmonies, and harmonies in, 285 origin of, 40, 286 peculiar characters of, 59 rudimentary organs of, 59, 60 Marinesco, on function of phagocytes, 241 Marriage, age at first, 97 Christian views on, 163 early, in primitive races, 86, 90 Martelly, on intestinal putrefaction, 255 Materialism, Büchner on, 220 Haeckel on, 220 Matriopathy, 6 May-flies and light, 35 Medicine, advance of, 210 Memory, late development of, 78 Ménière, on bees and orchids, 21 Menstruation, in monkeys, 88, 89 origin and significance, 87, 88 origin of, 89 regarded as impure, 92 Merkel, on tissue-changes in old age, 238 Metamorphoses, of ephemerides, 272 Metchnikoff, on blanching of hair, 242 on senile atrophy, 238 Metchnikoff, Madame, on tadpoles reared without microbes, 249 Meyer-Benfey, on happiness, 198 on immortality, 198 Microbes, absence of, in ephemerids, 274 harmful, 256 of the intestines, 248 producing poisons in intestines, 251 Microphags, definition of, 240 functions of, 240 Milk, fermented or soured, beneficent action of, 255 human, 282 secretion of, by males, 298 Monkeys, and choice of food, 75 Morality, based on human nature, 9 true foundation of, 289 Mosaic regulations on diet, 162, 163 Moths and light, 35 Müller, Johannes, on the eye, 78 Hermann, on lady-birds, 32 Max, on meaning of Nirvâna, 155, 158 Mutilations of the body, 9, 15 Naegeli, on natural death, 265 Natural death, 302 cases of, 278, 279, 280 in ephemerids, 27 Nature, Marcus Aurelius on life according to, 173 and morality, early opinions on, 3 Negroes and whites, 109 Nicene Creed, compared with ancestor-worship, 151