I recieved last night your favor of the 19th. and with it the pamphlet of Naval architecture for which I thank you. it may be of use in our navy office where I shall deposit it. I am extremely glad to hear that the infection from the vaccine matter I sent has succeeded. but my great anxiety now is to know whether it prevents the small pox: and my anxiety arises not from any doubt that it would prevent it if taken in a proper stage, but from an incertainty whether it has been continued genuine. I have great confidence it was so when I brought it here. I suppose it from the uniformity of all the cases, & from the certainty with which the matter always took effect. I suspect that when effete, it oftener fails to give any disease, tho’ it sometimes does give a spurious one. with respect to the publication of my letter, you observe it does not go at all to the only fact about which the world has any doubt, to wit, whether the vaccine disease prevents the small pox? I had no opportunity of trying that. it therefore would give no evidence on that subject. add to this that it is in a branch of science with which I have little acquaintance, have no pretensions to descant on, and that it gives no information sufficiently accurate to be of any service to a physician. I should therefore be entirely unwilling to have it presented to the public. the facts are free for use either in lectures, conversation or otherwise, and they may be mentioned on my observation if that will accredit them, because I believe them to be exact: but the publication of the letter would be entering an Arena on which I am not qualified to exhibit before the public. I shall be very glad to learn the effect of the variolous after the vaccine inoculation. Accept my respects & best wishes