"The yellow fever, as it appeared among the troops in Guiana and the West-India islands, in the years 1796 and 1797, exhibited such perpetual instability, and varied so incessantly in its character, that I could not discover any one symptom to be decidedly diagnostic; and hence I have been led into an opinion that the yellow fever, so called, is not a distinct or specific disease, but merely an aggravated degree of the common remittent or bilious fever of hot climates, rendered irregular in form, and augmented in malignity, from appearing in subjects unaccustomed to the climate. _Philadelphia, January 12th, 1798._" Many other authorities equally respectable with Dr. Pinckard's, among whom are Pringle, Huck, and Hunter, might be adduced in support of the unity of bilious fever. But to multiply them further would be an act of homage to the weakness of human reason, and an acknowledgment of the infant state of our knowledge in medicine. As well might we suppose nature to be an artist, and that diseases were shaped by her like a piece of statuary, or a suit of clothes, by means of a chissel, or pair of scissars, as admit every different form and grade of morbid action in the system to be a distinct disease. Notwithstanding the fever put on the eleven forms which have been described, the moderate cases were few, compared with those of a malignant and dangerous nature. It was upon this account that the mortality was greater in the same number of patients, who were treated with the same remedies, than it was in the years 1793 and 1794. The disease, moreover, partook of a more malignant character than the two epidemics that have been mentioned. The yellow fever in Norfolk, Drs. Taylor and Hansford informed me, in a letter I received from them, was much more malignant and fatal, under equal circumstances, than it was in 1795. There were evident marks of the disease attacking more persons three days before, and three days after the _full_ and _change_ of the moon, and of more deaths occurring at those periods than at any other time. The same thing has been remarked in the plague by Diemerbroeck, in the fevers of Bengal by Dr. Balfour, and in those of Demarara by Dr. Pinckard. During the prevalence of the fever I attended the following persons who had been affected by the epidemic of 1793, viz. Dr. Physick, Thomas Leaming, Thomas Canby, Samuel Bradford, and George Loxley, also Mrs. Eggar, who had a violent attack of it in the year 1794. Samuel Bradford was likewise affected by it in 1794.