The fever last treated of may be said to be peculiar to a hot climate; but the hot seasons of temperate climates produce something resembling it. That now to be described never occurs, so far as I know, except under the influence of tropical heats. Such a fever is indeed known without the tropics; for it is very common in Carolina in the hot season; but there the heat is even greater than that of the West Indies. In order to produce it, there must be, for some length of time, a heat seldom falling below seventy-five degrees on Fahrenheit’s thermometer. Though it differs from the fever last described, both in its causes and symptoms, it is not meant to say that it is so distinct as to form a separate species of disease, like the measles and small pox. Unless the characters of fevers are strongly marked, it is difficult, and even impossible, to refer them to any particular species; and the different concurrence of causes and constitutions is so various, that great numbers of ambiguous cases occur. With regard to the cause of the yellow fever, it differs from the bilious remittent in this, that the air of woods and marshes is not necessary to produce it; for it most commonly arose from intemperance or too much exercise in the heat of the sun. It was observable, however, that it was more apt to arise when, besides these causes, men were exposed to unwholesome air, particularly the foul air of ships, whether from infectious effluvia, or proceeding merely from the putrefaction that takes place in neglected holds. It is also remarkable with regard to it, that it is confined almost entirely to those who are newly come from a cold or temperate climate. The same remark is made by the French, who therefore call it _fievre de matelot_[101], considering it as peculiarly incident to those who have newly arrived from a long voyage. It would appear also, from what has been formerly mentioned[102] that those men, who have been exposed to that sort of infection that prevails in ships in cold climates are more particularly the subjects of the yellow fever when they arrive in a hot climate. It is farther in proof of the same opinion, that there are medical gentlemen, natives of the West Indies, who have hardly ever seen it, their practice lying at a distance from any sea-port town where strangers usually arrive. Of these strangers, those who are young, fat, and plethoric, are most apt to be attacked; and more of our officers in proportion were seized with it than common men. It has been said, that it never attacks either the female sex or blacks. This is in general, though not absolutely, true; for I knew a black woman, who acted as nurse to some men ill of this fever at Barbadoes, who died with every symptom of it.