From Andrew Clark   3 September 1873

My dear M^r. Darwin

I thank you exceedingly for your kind letter & acknowledge, as against myself, the wisdom of your resolution.¹

In my eagerness to get near to you I became partially blind; but with the just touch of an independent hand you have restored me to sight.²

Nevertheless I indulge the hope that the time will come when I may offer without indelicacy & you may accept without reluctance & without sense of obligation such small service as it is in my power to render you.³

I examined the urine with care: it is of good density & although loaded with uric acid it contains no albumen. The kidneys therefore are quite sound & I have no qualification to make of the statement that you are quite free from organic disease.—

It is not now difficult to see the way in which your troubles arise & make themselves manifest: there is first of all the acid indigestion, then there is the retention in the blood and in the tissues of acid waste stuffs*, and lastly as this retention now & then rises into a big wave it worries the nervous system and then breaks into a shower of uric acid which falls through the kidneys & escapes by the urine.—

The right method of managing this state of affairs is equally plain: we must diminish the manufacture and increase the output of acid stuff.— The one is to be done by attention to the quantity & quality of the food; the other by free action of the skin. Upon these two notes I have composed my diet score which will be handed to you by M^r. Willey.⁴ I hope you will practise it daily for a few weeks & that you will suspend your judgement of its merits for at least a fortnight to come. It will not suit you at once & even later it may need modification: there will be no getting to paradise without the passage of purgatory

If anything occurs to you pray let me hear from you & if you put your name in the corner of the envelope your letter will be forwarded.

Sincerely yours | A W^m Clark

i.e the “gouty” state.