In the short account of the yellow fever, which I left with you at Philadelphia, I have not endeavoured to establish any theory, or even to make any deductions from any established theory of that, or like diseases; but have only delivered a few matters of fact, as they occurred to me in practice, (which are chiefly or only such as I thought were either new or not well confirmed and known before,) as a foundation to build a theory upon, and on which to deduce a rational cure of this disease; and it is such which I humbly conceive may be most pertinent to the laudable designs of your society, of promoting rather that repeating the knowledge of the arts and sciences; nor have I either health or leisure at present, to deduce any theory or particular applications of it, from these data; however, I am glad to see myself so well prevented in this by your worthy colleague, Dr. Colden, as far as relates to malignant fevers in general, in this paper which you favoured me with. But as all diseases are generally attended with some peculiar and distinguishing symptoms, whereby they differ very materially from those of the same general denomination, especially in their cure, so I shall mention the concomitants of this disease, which seem to distinguish it as much from other malignant and pestilential fevers, and are to be had as much regard to in the cure, as the eruption of pustles in the measles or small pox, or of carbuncle and buboes in the plague; for beside the general affections of the solids and fluids, we must likewise have particular regard to the symptoms which they produce in the cure of diseases.

The first of these concomitants of our yellow fever, which is so material to be regarded, is an inflammation of the stomach, or liver, or both, with the adjacent parts. This appears not only from dissections, but from all outward symptoms or appearances of the disease, to be a most constant and aggravating circumstance of it; inasmuch that I never knew any one to die in this disease, without manifest tokens of this inflammation of the stomach or adjacent parts: this, as well as the inflammation of other viscera, generally of the brain, it is true, sometimes happens in other fevers of this class, but not so constantly, and almost surely, as in this. The next appearance of our malignant, or rather pestilential fever, as it may be called, which ought to be regarded, is an icterus, or yellow effusion. This, it is true, has imposed upon some so far as to make them take this symptom for a cause; to take this nominal, for the real essence of the disease; whereby they reckon this fever to be entirely of the bilious kind; but it would be equally wrong, and of as bad consequence almost, in practice, to have no regard to this most fatal appearance in the disease, as to deduce its nature solely from thence. These two constant concomitants of the disease, wherever it is severe and mortal, joined to the general state of the fluids, which is very well explained by Dr. Colden, may give us a good idea of this disease, and point out the several indications of cure. The principal of these indications, which has been so well explained by many, is sweating, or at least promoting a constant diaphoresis, well known to be necessary in all malignant fevers. But, alas! it is much easier to propose a general method, than to perform a cure, when we come to practice; for that accurate observer, Sydenham, tells us, that the method which will prove successful in one year, (not to mention particular cases) will be prejudicial in another. Thus, in the years 1737 and 1741, when this disease was epidemic in Virginia, the sick could not be made to sweat in the winter and spring seasons; at least, not so plentifully as was necessary to check the violence of the fever, and avert the impending inflammation; which, indeed, is very often the case, when this distemper is very severe; for you must observe, that it differs as much in degree, at different times, as the measles or small-pox does. All heating sudorifics, in these cases, bring on the inflammation, and hasten on the gangrenous state of the viscera; and plentiful bleeding (which I have known to be urged by some in these urging occasions) causes a no less fatal dissolution of the fluids, or mortal debility, both which are but too well known in practice, and are easily deduced from the theory of these diseases. It is upon such occasions, as you may perceive, that I recommend purging in this disease, agreeably to the practice of all physicians who have had any considerable experience in it; for there are no parts, through which the lymphatic humours (which, as Dr. Colden justly observes, are the principal seat of this distemper,) go off with more ease and more freely, than through the glands of the primae viae. Helvet. Anim. Econ.1

Another advantage, and even necessity of purging, is obvious to be perceived from the necessity of cleansing the primae viae of their feculent and corruptible contents, which is of great service, when they come to be so severely affected. When this alone is indicated, by purging it may be done without any danger of driving the humours to the bowels; for the action of lenitives is no more to be referred to purgation, than the washing of the skin is to be referred to the action of sudorifics. Pitcairn. Dissertat. de Febr. curat.2 But it is very certain, what Dr. Colden rightly inculcates, that purging in this disease, requires much medical skill and prudence, (as well as most other applications in it,) and ought not to be rashly attempted; for which reason I have been more particular in explaining the reasons of it, and wish I had leisure to be as particular in delivering the practical observations which confirm and illustrate this part of practice, and the cautions requisite in it; but in general it might be observed, that it is rather out of necessity than choice, that we have recourse to purging before, or rather, at the decline of this disease. But on the decline it is so necessary that I never knew the yellow effusion to be carried off, except in one single instance, without a purge; the reason of which appears to be the viscidity of the bile, which occasions this icterus, which cannot pass off by other outlets. Dr. Colden desires to know, if any recover after purging without sweats? I can inform him, that sometimes they do, although sweats are the most general critical evacuations of all fevers. But the miasmata of contagious fevers, seem to be so subtile, that when they are disengaged from the more viscid humours, they make their escape insensibly through the pores of the skin and other parts; by which you may see some recover suddenly and surprisingly, without the least perceptible evacuation. As to the relapse, which Dr. Colden thinks may proceed from the sick being exposed to the cold air after the fever, you must observe, that this was not an accidental, but a constant circumstance of the disease, at least at four times, when it has been epidemic in Virginia, and as much to be expected, as the return of an intermittent fever at its stated periods, whenever care was not properly taken to prevent it. What seemed to aggravate it most, was a too plentiful or gross diet. I imagined it might proceed from some lentor of the fluids, not removed nor evacuated, on account of the extreme debility of the body, which might afford, as it were, a nidus, for the subtile contagious vapours; in the same manner as some people, who have a great fluidity of their humours, and free execretions, never contract any contagious disease; whilst others, whose fluids are more viscid, can hardly avoid it, and suffer most severely from them.