19. Whoever observes these rules of life faithfully I guarantee him a long life without disease. He shall reach a good old age, and when he comes to die will not need a physician. His body will remain always strong and healthy, unless of course he has been born with a weak nature, or has had an unfortunate bringing up, or should be attacked by epidemic disease or by famine. 20. Only the healthy should keep these rules. Whoever is ill or a sufferer from any injuries, or has lost his health through bad habits, for him there are special rules for each disease, only to be found in the medical books. Let it be remembered that every change in a life habit is the beginning of an ailment. 21. If no physician can be secured, then ailing people may use these rules as well as the healthy. These rules are, of course, full of the common sense of medicine that endures at all times. For the tropical climate of the Eastern countries they probably represent as good advice as could be given even at the present time. With them before us it is not surprising to find that on other subjects Maimonides was just as sensible. Perhaps in nothing is this more striking than in his complete rejection of astrology. Considering how long astrology, in the sense of the doctrine of the stars influencing human health and destinies, had dominated men's minds, and how universal was the acceptance of it, Maimonides' strong expressions show how much genius lifts itself above the popular persuasions of its time, even among the educated, and how much it anticipates subsequent knowledge. It is well to remind ourselves that as late as the middle of the eighteenth century Mesmer's thesis on "The Influence of the Stars on Human Constitutions" was accepted by the faculty of the University of Vienna as a satisfactory evidence not only of his knowledge of medicine, but of his power to reason about it. At the end of the twelfth century Maimonides was trying to argue it out of existence on the best possible grounds. "Know, my masters," he writes, "that no man should believe anything that is not attested by one of these three sanctions:--rational proof as in mathematical science, the perception of the senses, or traditions from the prophets and learned men." His biographer in the monograph "Maimonides," published by the Jewish Publication Society of America[5], expresses his further views on the subject in compendious form, and then gives his final conclusion as follows: