In my attempts to teach the citizens of Philadelphia, by my different publications, the method of curing themselves of yellow fever, I observed no difficulty in their apprehending every thing that was addressed to them, except what related to the different states of the pulse. All the knowledge that is necessary to discover when blood-letting is proper, might be taught to a boy or girl of twelve years old in a few hours. I taught it in less time to several persons, during the prevalence of the epidemic. I would as soon believe that ratafia was intended by the Author of Nature to be the only drink of man, instead of water, as believe that the knowledge of what relates to the health and lives of a _whole_ city, or nation, should be confined to one, and that a small or a privileged order of men. But what have physicians, what have universities or medical societies done, after the labours and studies of many centuries, towards lessening the mortality of pestilential fevers? They have either copied or contradicted each other, in all their publications. Plagues and malignant fevers are still leagued with war and famine, in their ravages upon human life. To prevent the formation and mortality of this fever, it will be necessary, when it makes its appearance in a city or country, to publish an account of those symptoms which I have called the _precursors_ of the disease, and to exhort the people, as soon as they feel those symptoms, to have immediate recourse to the remedies of purging or bleeding. The danger of delay in using one, or both these remedies, should be inculcated in the strongest terms, for the disease, like Time, has a lock on its forehead, but is bald behind. The bite of a rattle-snake is seldom fatal, because the medicines which cure it are applied or taken as soon as the poison comes in contact with the blood. There is less danger to be apprehended from the yellow fever than from the poison of the snake, provided the remedies for it are administered within a few hours after it is excited into action. Let persons who are subject to chronic pains, or diseases of any kind, be advised not to be deceived by them. Every pain, at such a time, is the beginning of the disease; for it always acts first on debilitated parts of the body. From an ignorance of this law of epidemics many persons, by delaying their applications for help, perished with our fever. Let nature be trusted into no case whatever, to cure this disease; and let no attack of it, however light, be treated with neglect. Death as certainly performs his work, when he steals on the system in the form of a mild intermittent, as he does, when he comes on with the symptoms of apoplexy, or a black vomiting. Cleanliness, in houses and dress, cannot be too often inculcated during the prevalence of a yellow fever.