However inoffensive uniform heat, when agitated by gentle breezes, may be, there is, I believe, no record of a dry, warm, and stagnating air, having existed for any length of time without producing diseases. Hippocrates, in describing a pestilential fever, says the year in which it prevailed was without a breeze of wind[49]. The same state of the atmosphere, for six weeks, is mentioned in many of the histories of the plague which prevailed in London, in 1665[50]. Even the sea air itself becomes unwholesome by stagnating; hence Dr. Clark informs us, that sailors become sickly after long calms in East-India voyages[51]. Sir John Pringle delivers the following aphorism from a number of similar observations upon this subject: "When the heats come on soon, and continue throughout autumn, not moderated by winds or rains, the season proves sickly, distempers appear early, and are dangerous[52]." [49] "Sine aura, usque annus fuit."--_Epid. 3._ [50] Letter from Sir John Bernard to Dr. Floyer, p. 233. [51] Vol. i. p. 5. [52] Diseases of the Army, p. 5. of the 7th London edition. Who can review this account of the universal diffusion of the miasmata which produced this disease, its universal effects upon persons apparently in good health, and its accumulation and concentration, in consequence of the calmness of the air, and believe that it was possible for a febrile disease to exist at that time in our city that was not derived from that source? The West-India writers upon the yellow fever have said that it is seldom taken twice, except by persons who have spent some years in Europe or America in the interval between its first and second attack. I directed my inquiries to this question, and I now proceed to mention the result of them. I met with five persons, during the prevalence of the disease, who had had it formerly, two of them in the year 1741, and three in 1762, who escaped it in 1793, although they were all more or less exposed to the infection. One of them felt a constant pain in her head while the disease was in her family. Four of them were aged, and of course less liable to be acted upon by the miasmata than persons in early or middle life. Mr. Thomas Shields furnished an unequivocal proof that the disease could be taken after an interval of many years. He had it in the year 1762, and narrowly escaped from a violent attack of it this year. Cases of reinfection were very common during the prevalence of this fever. They occurred most frequently where the first attack had been light. But they succeeded attacks that were severe in Dr. Griffitts, Dr. Mease, my pupil Mr. Coxe, and several others, whose cases came under my notice.