I wish to mention to you in confidence that I have obtained authority from Congress to undertake the long desired object of exploring the Missouri & whatever river, heading with that, leads into the Western ocean. about 10. chosen woodsmen headed by Capt. Lewis my secretary, will set out on it immediately & probably accomplish it in two seasons. Capt. Lewis is brave, prudent, habituated to the woods, & familiar with Indian manners & character. he is not regularly educated, but he possesses a great mass of accurate observation on all the subjects of nature which present themselves here, & will therefore readily select those only in his new route which shall be new. he has qualified himself for those observations of longitude & latitude necessary to fix the points of the line he will go over. it would be very useful to state for him those objects on which it is most desireable he should bring us information. for this purpose I ask the favor of you to prepare some notes of such particulars as may occur in his journey & which you think should draw his attention & enquiry. he will be in Philadelphia about 2. or 3 weeks hence & will wait on you.

I have owed, now a twelvemonth, an answer to your very friendly letter of Mar. 12. 1802. but when certain things press, & others will bear delay, we naturally take up the former, & the latter lie over. after all my life having enjoyed the benefit of well formed organs of digestion & deportation, I was about 2. years ago taken with a diarrhoea, after having dined moderately on fish which had never affected me before. in the course of 2. or 3. weeks it wore me down by the frequency of calls, but then got so much better as to call on me but once a day, but still of watery consistence, and distressing me with troublesome borborygmi. for a twelvemonth past however, these circumstances are more favorable, and tho’ they continue to a certain degree, I enjoy good health. in the course of it I have made experiment of every kind of diet, drink & regimen: and I find that fish is the only article which affects me; & what is remarkeable while fish & sturgeon affect me powerfully, neither oysters nor crabs do. I find it important too to be moderate in the quantity of food. the stomach has never failed in the least, but performs it’s functions most perfectly: the bowels alone are weak and labour in their operations. I have troubled you with these details because your friendship called for them. I have found that riding is my remedy. a journey brings me to my antient habits for some days, and daily rides of an hour or two keep me free from inconvenience from the visceral weakness. I see at present nothing more in it than a liability to a return whenever an unfavorable affection occurs in any part of my system. I doubt the effect of medecine in chronical1 cases of this kind at any period of life, & still more so at mine. the system however may perhaps gradually recover it’s strength. but these unlettered ideas are laid at your feet: your information & experience will regard nothing but the facts; and certainly my confidence not only in your skill but your friendship will render truly valuable to me any ideas which you can without trouble throw on paper, for my government in the event of a return of the complaint to a troublesome degree: for at present it exists only2 in a perfectly innocent state. I pray you to accept assurances of my affectionate friendship & sincere respect.