PART III

INVESTIGATIONS ON NATURAL DEATH

I

NATURAL DEATH AMONGST PLANTS

Theory of the immortality of unicellular organisms.—Examples of very old trees.—Examples of short-lived plants.—Prolongation of the life of some plants.—Theory of the natural death of plants by exhaustion.—Death of plants from auto-intoxication 94

II

NATURAL DEATH IN THE ANIMAL WORLD

Different origins of death in animals.—Examples of natural death associated with violent acts.—Examples of natural death in animals without digestive organs.—Natural death in the two sexes.—Hypothesis as to the cause of natural death in animals 109

III

NATURAL DEATH AMONGST HUMAN BEINGS

Natural death in the aged.—Analogy of natural death and sleep.—Theories of sleep.—Ponogenes.—The instinct of sleep.—The instinct of natural death.—Replies to critics.—Agreeable sensation at the approach of death 119