One attack of yellow fever gives such great protection that, in practice, a man who can prove that he has once had the disease is looked upon as entirely safe. But of course he has to prove this to the satisfaction of the quarantine physician. It is considered so certain that everyone exposed to yellow fever will have the disease that proof that a man has lived in an endemic center for ten years is accepted as proof of his immunity. No quarantine is, however, absolute in any disease, in any locality, or carried out by any authority. Some people now and then will pass the quarantine who are either so slightly sick that the disease is not recognized, or who developed the disease after they had been released from quarantine. But a quarantine greatly lessens the number of times and the frequency with which infection is introduced into a locality. For some reason yellow fever, in the minds of people generally, is covered with a cloak of mystery. In communities where it prevails there are hundreds of remedies and courses of treatment that are vaunted as being infallible cures, and the more ignorant and uneducated the possessors of these specifics, the more readily they seem to be accepted by the people generally. But yellow fever, like every other acute disease, has its own natural history, and man at present knows no remedy that can shorten or change its course. Many a time I have found myself completely routed in cases of yellow fever by the old negro mammy, who would insist that if the patient would take orange-leaf tea and adopt certain other procedures which she advocated, the patient would certainly get well. Now, on the average with severe yellow fever, seventy-five per cent. will recover and twenty-five per cent. will die. The negro mammy did not know this, but was firmly convinced that it was the orange-leaf tea which caused the recovery in the cases of those who recovered, and some departure from her directions that caused death in the case of those who died. She believed that if her routine had been carried out in the fatal cases, they would have recovered. I must confess, however, that in my experience the measures generally advocated by the negro mammy did little or no harm, and in looking back over a yellow-fever experience of thirty years, I cannot by any means make so strong a statement with regard to my professional brethren. One of the most general superstitions with regard to yellow fever was that all air must be kept from the patient. With this in view, the room in which the patient was treated was kept closed and entirely dark. No water for washing the face and hands, no change of body or bed clothing was allowed during the course of the disease. The conditions, therefore, as to filth when a patient had been ill five or six days can be better imagined than described.