Mesnet and Mottet, Drs., cases of hysteria, 203 Mice, duration of life, 41, 43, 56 Michaelis, on muscles of monkeys, 185 Microbes, as cause of senility, 73 in food, 162, 163 passage through intestinal walls, 71 _Middlemarch_, G. Eliot’s, 322 Milk, importance of boiling, 177, 178 microbes of disease in, 177 putrefaction and fermentation of, 167 use of soured milk, 181, 182 Mill, J. S., 323 Milne-Edwards, H., on laws of duration of life, 42 Minot, Prof., on cause of old age, 16 Moa, 213 Moebius, on Goethe, 271 on Schopenhauer, 255 Molluscs, ages of, 48 Mongols, hair in old, 17 Monkeys, longevity of, 83 Monsters, double, 216 _Monstrilla_, life-history of, 115, 116, 117 Montefiore, Sir M., 91 Morality, Christian, 321 definitions of, 303 Kantian, 309, 310, 311, 312 science and, 301 _et seq._ Mortality rates of old persons, 142, 143 Moses, use of soured milk, 171 Mosso, on fear, 194, 196 Muscles, degeneration of, 9, 26, 27 Myxomycetes, 215 Naegeli, on age of trees, 99 Nails, growth of, in the old, 18 Naphthaline, as an intestinal antiseptic, 156 Nature, human, 325 Nausenne, Mde., cause of longevity, 141 Negroes, longevity of, 88 Neisser, Prof., on protection against syphilis, 146 Nematodes, death of, 111 _Nemertines_, life-history of _Pilidium_ of, 109 _et seq._ Nencki and Sieber, on digestion, 153, 161, 169 Neuronophags, 19, 20, 21, 22, 23, 24 Nicotine, use of in experimental production of atheroma, 32 Nietzsche, criticism of Socialism, 230 Nogueira, M., on use of soured milk in Africa, 172, 174 Obstacles, sense of, 258 Old age, Goethe and, 279 _et seq._ Olympian, Goethe as an, 269 Optimism, foundation of, 256 Goethe’s transformation to, 269, 270 _et seq._ Orang-outan, 185, 193 Orotava, dragon-tree of, 96 Orstein, Dr., on centenarians in Greece, 90 Orthobiosis, 212, 325 _et seq._ Ossetes, use of soured milk, 173 Osteoclasts, 30 Ostrich, defecation of, 76 Oustalet, M., on longevity of vertebrates, 46 Ovary, atrophy of, 26 Owls, intestinal flora of, 83 Ownership, collective, 229, 230 Parodi, on old age, 332 Parr, Thomas, 87 Parrots, duration of life, 41 scanty intestinal flora of, 79 Pasquier, Dr. du, on constipation, 67 Pasteur, discovery of lactic microbe, 105, 167 Paulsen, criticism of Kant, 314 Pensions, old age, 3, 4, 133 Pessimism, 129, 233, 234, 239, 241, 249, 266 Pessimist, study of life-history of a, 249 _et seq._ Pflüger, on longevity, 93 Phagocytes, 18, 19 Phagocytosis, examples of, 25, 37 Phalansteries, 229 _Pilidium_, 109 _et seq._ Pitres, M., hysteric patients of, 200 Plague, 323 Plants, death of, 99, 103 Plasmodia, of Myxomycetes, 215, 216 _Pleurotrocha haffkini_, 112, 113 Pochon, Dr., experiments on use of lactic bacilli, 169 Poehl, Dr., on spermine, 139, 140