It is fortunate for Mankind when those who possess splendid Talents, and who are placed in high political Stations continue to devote a part of their time to the Sciences. It is thus peculiarly gratifying to a benevolent Mind to discover in you a Solicitude to advance those Sciences that tend to the Benefits of Society.

The Ravages made in our Country by the yellow Fever have been truly affecting, not only as they respect the loss of many valuable Individuals, but in severing the Bonds of social Felicity, and to prevent its Effects some of our populous Cities have been several times for short periods nearly abandoned. The Inconveniences to which Society is subject, are also very extensive, for beside the Interruption of communication between places intimately connected the Interruptions of Commerce by the Quarantine Regulations have been very injurious to our Merchants in every part of the Union. It was a subject therefore well worthy of the Attention of our Chief Magistrate, and your considering the supposed contagious Matter within the power of chymical Correction was a phylosophical Conclusion supported in my Opinion by many Facts. I have examined Guyton-Morveau’s “Traité des Moyens de désinfecter l’air, de prevenir la Contagion et d’en arrêter les Progrès”, with which you condescendingly favoured me. This Work contains so many Instances of success in compleatly destroying putrid and noxious Effluvia by impregnating tainted or corrupted Air with different Gauzes, that it appears to me almost impossible to doubt their Efficacy.—

I have long been of Opinion, and almost every Observation tends to confirm me in the Idea, that the Yellow Fever is produced in this Country as well as in other places. We know that Vessels from the same port in the West Indies which arrived at different Ports in other Countries, have in some Cases appeared to infect the ports where the Men and Goods were landed; while in other Ports no such Effect followed. We know from long Experience and almost numberless Instances that Individuals actually affected with the yellow Fever have gone from infected places in our Cities to healthier places in the Country, and have there recovered: also that others so far advanced in the Fever as to die after being removed into the Country have not even affected those who not only constantly attended them but who laid in the same Beds, and received their dying corrupted Breathes—A Physician in Philada.   attended Patients in the Hospital who were in all stages of the Fever: he received their breaths: he laid in the same Bed with those dying: he inoculated himself with, and swallowed some of the black bilious Vomit of those who died, yet remained unaffected with the Fever: he went into a part of the City where the Fever raged, was affected & died! The Nurses in the Hospital of Philada. which was an airy clean place were happily preserved, though they were subject to an Air tainted to a certain degree, but not sufficiently to produce the Symptoms of Fever.

We read in the Accounts of Egypt of Regiments being affected with the Plague, and, many dying, while others were removed to healthier places, who, though affected, recovered.—Other regiments were sent into the Stations of those removed, and were not affected with the Plague till they had resided there some weeks. The impure Air affected them slowly, but with certainty. On removal they also recovered.—In the West Indies, in bilious, intermittent, remittent, or continued Fevers, when the most efficacious Remedies of the Materia Medica have in vain been tried, and Death stands in the Portals of Eternity, beckoning to languid Mortality, the Physicians direct their Patients to be carried to the Mountains, where Death seldom follows them. In a high region where they breathe a pure, cool Air, refreshed by every Breeze, they begin very soon to recover: but while they enjoy this Benefit nothing is neglected. The Physicians of the Islands know that any neglect is fatal, & therefore they are perhaps the most attentive of any in the World; they watch with Care every Change, and not only administer Remedies, but are exceedingly attentive to give regular Supplies of light but rich nourishment, and in Cases of necessity they pushed the diffusible Stimuli with a freedom that would surprise the boldest Sons of Galen.

The Plague is classed among the Specific Contagions. The Facts reported from Egypt tend to throw some Light on the Subject of Specific Contagious-Matter. If the Plague become a specific Contagion, and is yet generated by the noxious Effluvia of corrupt Matter whether Vegetable or animal or both, or by any absorption of the oxygen of the Atmosphere, or by a disproportioned quantity of azote to the oxygen or pure Air; if healthy Bodies without Infection from others can be, by Situation alone affected with the Plague, and are capable of producing it in others, who, though predisposed, might never otherwise have had that peculiar type of Fever, may we not suppose that other Disorders which appear to affect the System by specific Types may also be originally produced by Miasmata, or by Situation Where the Air undergoes noxious changes with respect to its component parts, or both, with such concomitant Circumstances as unwholesome Diet, relaxation by excessive heat, moisture, & the want of Exercise? May not also the prevalence of some of those Causes give complaints of one Type, & the prevalence of others vary the Type? And may we not, in the same manner attribute the fatality of the Small pox to the specific quality of the matter taken from the Cow of one Country, where the Animal may have been subject to noxious Vapours, & consequent violent Eruptions, while in the Mild vaccine Matter, now substituted, we find nothing dangerous, because communicated from Cattle but slightly affected with the Disease, and otherwise in a healthy State? Or the small Pox may have been derived from good matter originally, for in the East, according to the accounts given by Lady Mary Wortley Montagu, it was a very mild Disease; but it may have become more dangerous by a vitiation of the Matter in passing through impure human Bodies, & a recurrence to the original Source is necessary, & will probably in time require repetition.—May not various other Disorders now considered as specific owe their origin to domestic Animals, together with a peculiarity of food & Climate?—The Leprosy & Measles may be communicated to Man from Hogs. Siphilic Complaints may originate in Dogs, as well as that peculiar Species of communicable Madness called Rabies Cannia, which however is so difficutly communicated to Man that not one in a hundred of the human Species will go mad if bitten by Dogs in the highest stage of the Disease. Thus Nostrums of prevention have gained high reputation without producing any Effect whatever.—May not many Diseases of a contagious Nature in the Course of time by propagation partake of other Disorders which Circumstances may have joined, and thus appear under a new Form or Type, & may we not under strict regulations & particular attention to the salutary Laws of Life with which Chemistry & Philosophy have made us familiar promise ourselves a radical Extermination of half the Ills of Life? I believe we may, but it requires some Effort to first eradicate our Prejudices.—

If we admit that the Yellow Fever is infectious we must also admit that it is generated in the West Indies & in Africa. What Causes induce its existence? Heat, Moisture, Miasmata, or a particular State of the Air with regard to its component parts. Any of these Causes or all of them combined may produce it in the Countries of which we speak. Have we not the same Causes in our own Country? Have we not a Heat which raises the Thermometer of Farenheit to 90 or 100 Degs. Have we not also Moisture, sometimes even Inundations from the copious Falls of rain—moisture from Mill ponds—from the rise—& fall of the Tides on the Coasts, where large tracts of Land are left in a humid State, and where Musketos & other Insects & Reptiles swarm—Have we not Miasmata rising from our Marshes in the Country, and from Brick-ponds, sewers &c in or near the Cities; and do we not suffer from the violent Intermittent Fevers, which cease the Weak, sometimes the Day that the Sick remove to places acknowledged healthy?—We have all these, and many other Causes not noticed or known.—How easy then to admit the generation of the yellow Fever in this Country! If the sameness or similarity of Causes be acknowledged, and the production of the Fever not acknowledged, it must depend upon their interruption by Winter, which braces the Body. But I am not of this opinion believing a few Weeks sufficient to produce it. And besides the common Causes I would add that there are the immense quantities of Vegetable Matter brought into the Cities every Autumn, but most abundantly in those Years when the Fever is the most destructive; for the very causes that destroy Animal promote vegetable Life.—The Offals of these Vegetables with the Water in which they are boiled, are also thrown into the common Sewers or Privies, and if a calculation were made of the impure Air produced by these Causes in addition to the common Causes which abound in our Cities, we shall have no occasion to attribute to foreign Aid the production of the Evil.—

Many contend that all these noxious powers are insufficient to produce the Fever, & that it is of an infectious kind, that the Causes mentioned are only sufficient to produce a predisposition to the Disease, that an active virus of a specific quality is necessary to produce the actual Disease, and that this is brought from the Torrid Zone, as they imagine they can in many Instances trace the Sources of Infection & the fatal Effects of its communication. Others contend that from Experiments tried it cannot be communicated, and thus Men of great Talents & Genius have differed in opinion, who considering more attentively all the relations and Circumstances would perhaps more nearly have coincided. These Disputes have been in some Degree beneficial, because they have led to a variety of treatment, & those who have had good opportunities of weighing well the results of the various modes of treatment have doubtless made valuable deductions. But these Disputes have likewise in some Instances discredited the Faculties of the Faculty.

I have noticed in some Practitioners a conviction that at certain Periods every Fever was the Yellow Fever in a greater or less degree, & the same Remedies were prescribed.—The Symptoms of the Yellow Fever were generally such as to induce a belief that it was a highly inflamatory Disease: Copious Bleedings were therefore directed, with Emetics, Cathartics, Sudorifics, Diuretics, &c. Sometimes Mercury was given in such quantities as to salivate. By these Modes healthy People might be brought to the grave, & I have no Doubt that hundreds of People who had no Disorder but the fear of having a Disorder became untimely Victims to medical Whims. Patients by this treatment would be brought to such a State of Debility that nothing could afterwards raise them: and in the first Stage of Disorder many Cases were not sufficiently marked to determine with certainty the propriety of such violent measures were they even proper in the yellow Fever: but I deny the salutary Effect of such treatment in the Yellow Fever, and instead of bleeding generally would only recommend it in some very inflammatory Cases, and would rely more on the warm Bath, with an Emetic, copious Cathartics, gentle Diuretics, Draughts impregnated strongly with the Carbonic Acid, and a constant supply of pure fresh Air; or if the Situation deny this let vital Air by artificial means be used freely, and let the nourishment be light. As soon as the inflammatory Diathesis diminishes, let the treatment vary by degrees, and according to the indications of approaching asthenic Disease begin with gentle Tonics varying the Powers as the general Indications vary, and increasing the strength & quantity of nourishment accordingly.—There are frequently Fevers of a malignant kind which appear very inflammatory in the first Instance, and if the depletive System were to be pursued, as now practiced, I know that Death would frequently offer his cold Hand to lead such Persons to the Grave; and the Physician might say with the Priests in Russia, who, when baptizing Children by dipping them into the River through a hole in the Ice, on being sometimes benumbed by the cold as to let the Child fall in—“hand me another for God has taken the last to himself.”

Admitting that the yellow Fever is imported, & the mode of cure correct, (both of which, in parenthese, I deny) that Fevers generated in the West Indies or in Africa of the Typhus kind, or the plague itself from the Levant ought to be guarded against by quarantine, the question you asked me impresses itself with great force. Would the present mode of performing Quarantine be sufficient to prevent the diffusion of noxious or contagious Diseases, or Effluvia, were such actually brought by the People or the Goods of our Vessels? My Opinion is decidedly in the negative: for the goods remain undisturbed on board, and we know that Goods opened many Months after they are packed up will still diffuse the noxious Matter with which they were primarily impregnated. My Opinion therefore coincides with yours, that instead of Vessels performing Quarantine it would be more safe to place the Goods & Cloaths in Warehouses prepared expressly for their purification, with the muriatic Acid Gas, obtained by pouring the Acid of Sulphur on common Salt; the Kali of which having greater affinity with this Acid than with the Acid with which it is naturally combined, the moment the Sulphuric Acid comes in contact with the common Salt a chymical Attraction or combination takes place, and the Acid of Salt, called the muriatic Acid, is extricated, and expands itself in the Air, which it is said compleatly to disinfect.—Thus the Holds of Vessels might be purified at a very small expense, & without detaining the Vessel; which, in a commercial view, is of great Consequence; but as this Air is not respirable, though recommended also for Hospitals by Monsr. de Morveau, it is not so eligible in my Opinion, in cases of Sickness as the nitric Acid Gas, expelled in the same manner from Nitre, & which has been so successfully used by many of the English Physicians, & also in Spain, in consequence of their writings.—I have also no doubt, from the number of successful Experiments made that the use of this Air would be highly beneficial in every species of pestilential Fever.—From the Experiments made by Morveau and others, and from the want of efficacy in Egypt in attempting to disinfect and purify noxious Air by white-washing with Lime I am of opinion it ought not to be depended on, though strongly recommended by some very able and learned Individuals.—I have however seen very surprising Cures by dipping and frequently washing the Body in Lime Water, in alarming Eruptions: and quicklime mixed with fixed Alkalies absorb correct or prevent the Effluvium of Sewers most compleatly, as I have often experienced.

I have the honor to be Sir with the highest respect yr. &c