When I entered upon my employment, the Commander in Chief gave an order, that every surgeon in the fleet should send me a monthly return, stating the degree of prevalence of different diseases, the mortality, and whatever else related to the health of the respective ships. This was done with a view to enable me to regulate the reception of men into hospitals, so that each ship might have a due proportion of relief, according to the degree of sickness on board, taking care at the same time that the hospitals should not be overcrowded; and also to acquaint the Commander in Chief, from time to time, of the state of sickness, or the predominance of particular diseases, in order to recommend such articles of diet, or other means, as might tend to cure them, or to check their progress. These returns have served also in this work as a method of collecting a multitude of well-established facts, tending to ascertain the causes and course of disease. While the fleet was in port, I also superintended and visited daily the hospitals, of which there is one at almost every island on the station; and having kept an account of the different kinds of disease that were admitted, and of their mortality, I have in this way likewise been furnished with a number of facts that may throw light on the history of human maladies. Nevertheless, I do not boast of having made great discoveries; and every person of a correct judgement must be aware how difficult it is to ascertain truths, and to draw fair and solid inferences, on medical subjects. I have attempted little more than to amass, from my own observation, and by the assistance of the surgeons of the fleet, a number of well-established facts, and to arrange them in such a methodical manner, as to prove a groundwork for investigation; and I am persuaded that others, of more sagacity and enlarged knowledge than myself, may be able to deduce from them, observations that may have escaped me especially if these new, but imperfect, attempts should come to be compared with similar ones that may be made by other observers in other climates, and in other circumstances of service. I met with several obstacles in instituting inquiries, purely medical, to the extent I could have wished. There is, in the first place, from the nature of the subject, a great difficulty attending all practical inquiries in medicine; for, in order to ascertain truth, in a manner that is satisfactory to a mind habituated to chaste investigation, there must be a series of patient and attentive observations upon a great number of cases, and the different trials must be varied, weighed, and compared, in order to form a proper estimate of the real efficacy of different remedies and modes of treatment.