WHAT SCIENCE CAN DO AGAINST DISEASE 203 Formation of the experimental method—The intervention of religion in disease—Disease as a basis of pessimistic systems of philosophy—Advance of medical science in the war against disease—The revolution in medicine and surgery due to the discoveries of Pasteur—The beneficial results of Serum Therapy in the war against infectious diseases—Failure of science to cure tuberculosis and malignant tumours—Protests against the advance of science—Opposition of Rousseau, Tolstoi and Brunetière—Proclamation of the fallibility of science—Return to religion and mysticism CHAPTER X INTRODUCTION TO THE SCIENTIFIC STUDY OF OLD AGE 228 General account of old age—Theory of senile degeneration amongst unicellular organisms—Conjugation amongst infusoria—Old age in birds and in anthropoid apes—General characters of senile degeneration—Sclerosis of the organs—Phagocyte theory of senile degeneration—Destruction of higher elements by macrophags—Mechanism of whitening of the hair—Serums acting on cells (cytotoxins)—Sclerosis of the arteries and its causation—Harm done by the microbes of the alimentary canal—Intestinal putrefaction and the modes of preventing it—Attempts to prolong human life—Longevity in biblical times CHAPTER XI INTRODUCTION TO THE SCIENTIFIC STUDY OF DEATH 262 Theory of the immortality of lower organisms—Immortality of the sexual cells in higher organisms—Immortality of the cellular soul—Occurrence of natural death in the case of certain animals—Natural death in the Ephemeridæ—Loss of the instinct of preservation in adult Ephemerids—Instinct of life in the aged—Instinct of natural death in man—Death of old men in biblical times—Changes in the instincts of man and lower animals CHAPTER XII SUMMARY AND CONCLUSIONS 285 Disharmonies in the human constitution as the chief source of our sorrows—Scientific data as to the origin and destiny of man—The goal of human existence—Difficulties in the way of scientific investigation of the problem, What is progress?—Difficulty of including the whole human rate in a scheme of progress and morality—The instincts of life and of natural death—Application to real life of the doctrines set forth in this book ILLUSTRATIONS