The late discoveries in England and Turkey of the beneficial effects of the kine pox, as an effectual preventive remedy, for the diseases of the small pox, and the plague; have irresistably led me to the following reflections.

The characteristics, that belong in common to both these complaints; appear to be—a power of seizing the human species but partially; by succeeding in their attacks on some, but becoming repulsed by others—of appearing only in hot weather; with a few exceptions to the small pox—when the putrescent tendency of the fluids, is most increased by heat—and, that they are both fevers; the one eruptive, and the other putrid.

From this data; the cause of the benefical effects of the vaccine innoculation, appears probable to be owing to some partial change of the fluids of the constitution, that the subject undergoes, approaching to the less putrefactive state of the fluids of the graminivorous animal, from whom the remedy is taken; that secures him uninjured, from the subsequent morbific attacks of these diseases; either, in inhaling an atmosphere impregnated with their effluvia, or in an innoculation of their diseased matter.

However, as the vaccine innoculation is proved to be a remedy against two violent fevers—the small pox, being commonly violent, when commencing without innoculation; it is no more than reasonable to infer, that, against other fevers of a similar nature, it will produce the same effect!—And, but few will venture to assert, that the small pox and plague, are more similar, than, the plague and yellow fever!

I cannot therefore, help being of the opinion, that it is likely to prove a remedy also; for this formidable calamity of the western world.

It would give me great happiness, to become the fortunate man of accelerating the discovery of a remedy, for so great an evil.

The most satisfactory trial of it, would be, by innoculating the matter of the yellow fever on a subject, that has been prepared for it, by the vaccine innoculation; but the danger that must attend the experiment, may be considered as putting it out of the power of any one to try it, yourself alone excepted, by having the lives of condemned criminals at your disposal.—Which necessitates me to trouble you with the affair.

I conclude it is unnecessary to send you a detail of the effects of the vaccine innoculation against the plague, as it has passed into most of the papers of the States.

I shall be obliged to you to inform me whether you think favorably enough of it, to induce you to give it a trial. You will also much increase the obligation, by informing me of the present condition of the breed of Arabian horses in Virginia; and to what degree they have arisen, as an article of comm[erce?] since the account you published of them, in your Notes on that State: And of the original stock was imported from south Arabia.

With the highest esteem, I have the honor to be Sir, your most obedient Servant