Out of the whole _Materia Medica_, I have chosen but very few medicines, and these I have confined myself to throughout the whole book. Many surgeons at sea will not, I know, be contented with so small an assortment; and I remember the time that such an observation might have been applicable to myself; but as I have by long experience learned to shake off prejudices, and been taught by the help of philosophy to pry into the nature of things in general, I solemnly declare, that now, I would venture to go to any part of the globe, not only with that little assortment of medicines I have mentioned, but even with many less. The _emetick tartar_, _sublimate mercury_ and the _bark_ are powerful medicines; but they should be in very skillful hands, otherwise they are rank poisons, and therefore I have omitted them here; but strictly speaking, every good medicine is the same. I have two maxims in physic, which I strictly attend to; one is, that to my friends I give the least medicines; the other is, that the principal virtue of a medicine depends on its application. The form of the medicine box, I have constructed so as it appears to me most convenient and handy; and every kind of medicine, I would advise to have labeled with their proper names, as well as with another mark that may take the eye at first sight; and the more to prevent mistake, one label should be fixt on the pot that contains the medicine, and the other on the box: for in medicines too much caution cannot be used. One thing with respect to the medicines, I have omitted, and that is their quantity requisite for the box, and their prices: I intended to have taken notice of this, but found that that could not with exactness be ascertained, unless entering into another subject, and that would take off from the conciseness of my plan. As I have however many other things respecting the benefit of seamen to offer, peculiarly respecting distant climates, I shall take notice of this, where it may come in, more pertinently to the subject: till then, that must be left to the management of the apothecary who is applied to for fitting out the box. If he is a man of candour and judgment he cannot be much out of his calculation, when he knows the number of hands, and the voyage intended. With respect to the other lectures, I have, as near as it was practicable, divided them into their different classes and sections; at the same time the whole is so linked together, that one lecture must support the other. And as I have throughout the whole course of the book differed more or less from the general mode of practice, I must hereby declare, that I have in this consulted my own experience more than any other authority, without fear of censure, or hope of applause, any farther than of truth, and my own conscience.