4. It has been a misfortune in medicine, as well as in other sciences, for men to ascribe effects to one cause, which should be ascribed to many. Hence diseases have been attributed exclusively to morbid affections of the fluids by some, and of the muscles and nerves by others. Unfortunately the morbid states of the arterial system, and the influence of those states upon the brain, the nerves, the muscles, the lymphatics, the glands, the viscera, the alimentary canal, and the skin, as well as the reciprocal influence of the morbid states of each of those parts of the body upon the arteries, and upon each other, have been too much neglected in most of our systems of physic. I consider the pathology of the arterial system as a mine. It was first discovered by Dr. Cullen. The man who attempts to explore it, will probably impoverish himself by his researches; but the men who come after him, will certainly obtain from it a treasure which cannot fail of adding greatly to the riches of medicine. AN ACCOUNT OF THE _STATE OF THE BODY AND MIND_ IN OLD AGE; WITH _OBSERVATIONS ON ITS DISEASES_, AND THEIR REMEDIES. Most of the facts which I shall deliver upon this subject, are the result of observations made during the term of five years, upon persons of both sexes, who had passed the 80th year of their lives. I intended to have given a detail of the names, manner of life, occupations, and other circumstances of each of them; but, upon a review of my notes, I found so great a sameness in the history of most of them, that I despaired, by detailing them, of answering the intention which I have purposed in the following essay. I shall, therefore, only deliver the facts and principles which are the result of the inquiries and observations I have made upon this subject. I. I shall mention the circumstances which favour the attainment of longevity. II. I shall mention the phenomena of body and mind which attend it; and, III. I shall enumerate its peculiar diseases, and the remedies which are most proper to remove, or moderate them. I. The circumstances which favour longevity, are, 1. _Descent from long-lived ancestors._ I have not found a single instance of a person, who has lived to be 80 years old, in whom this was not the case. In some instances I found the descent was only from one, but, in general, it was from both parents. The knowledge of this fact may serve, not only to assist in calculating what are called the chances of lives, but it may be made useful to a physician. He may learn from it to cherish hopes of his patients in chronic, and in some acute diseases, in proportion to the capacity of life they have derived from their ancestors[67].