Not being a native of, or even resident in, either America or England, though possessed of a fair knowledge of the English language—having delivered addresses in several universities, and before numerous medical societies in the United States, Canada, England, and Scotland—it was very difficult for us to avoid idiomatic errors. We take great pleasure in acknowledging, therefore, our indebtedness to our friend, Col. Frank Haddan, of London, who, being impressed with the importance of our subject and its humanitarian aspect, kindly volunteered to look through our manuscript and correct most of our errors of style and grammar, thereby rendering us valuable assistance. Our thanks are also due to Dr. Leo Rosenthal, of New York, for the adjustment of many technical sentences. Every one will admit that the subject treated in this work is not an easy one. It might be urged also that its presentation here is based on entirely novel lines, scientific literature on old age being very scarce. Considering also that it has been necessary for us to take up questions beyond the ordinary sphere of a medical practitioner, sometimes of a philosophical, technical and physical nature, it is to be expected that certain imperfections will be found. But, whatever may be the opinion of the reader, he will not deny that none should fail to derive some benefit from the numerous hints we have given for the preservation of health and prolongation of life. If by reason of our advice we succeed in saving but a single human life from a premature grave, our aim will have been attained. DR. ARNOLD LORAND. ------------------------------------------------------------------------ CONTENTS. ─── CHAPTER I. PAGE ON THE APPEARANCE OF SYMPTOMS OF OLD AGE IN YOUNG 1 PERSONS CHAPTER II. ON THE AGENCIES WHICH GOVERN OUR EXTERNAL 11 APPEARANCE AND THE NUTRITION OF THE TISSUES CHAPTER III. ON THE AGENCIES WHICH GOVERN IMMUNITY AGAINST 21 INFECTIONS AND INTOXICATIONS—THE ORIGIN OF FEVER CHAPTER IV. ON THE AGENCIES THAT GOVERN THE CONDITION OF THE 35 NERVOUS SYSTEM AND MENTALITY CHAPTER V. ON THE INFLUENCE OF THE SEXUAL GLANDS UPON 45 VITALITY AND LONG LIFE CHAPTER VI. ON HEREDITY AND LONGEVITY 55 CHAPTER VII. ON MEANS WHICH CAN HELP US TO DETERMINE THE 64 PROBABLE DURATION OF LIFE CHAPTER VIII. ON THE CAUSATION OF OLD AGE 90