To T. L. Brunton   11 May 1874

My dear Dr Brunton

Will you add to your former kindness by examining the enclosed slide, gummed to the lid of the box, & then throw it away. It is a minute whitish floculent mass which I want you look at; & the spec. nearest the label is the best. I put minute drop of skimmed milk on the glands of drosera, & it became, as usual, curdled in about 10^m. After from 6^h.— to 8^h a large part of the curds was dissolved & disappeared. It is the remnant scraped off the leaf, with water added, which I want you to look at. I suppose that it consists of oil-globules. I coagulated, for comparison, a small drop of skimmed milk with acetic acid, & found much floculent matter, which I suppose from your book to be Casein. This Casein has all disappeared from the milk subjected for 2 days to the secretion of Drosera, & the oil globules are larger & less regular than in the milk curdled by acetic acid. All that I want to know is, whether I am right in what I have here said.¹

There is one other question; I find that if I add a minute drop of Hydrochloric acid of the strength of 1 to 100 of water to the secretion on the leaves, it stops their digesting minute cubes of albumen; but if I add to the secretion minute drops of the strength of 1 to 200 of water, the albumen is all dissolved. Does this different action agree with that of pepsine & H. acid? I presume that artificial digestive fluid fails to digest if it be weakened with a great excess of water²

Pray excuse my troubling you & believe me yours very sincerely | Ch. Darwin

P.S. When I asked you about Urea, I had stupidly forgotten my own observations; I tried it in solution to ascertain whether this refuse product of an animal would act on Drosera; & it did not, any more than gum or sugar   My trial had no relation to digestion.—³

Two specimens of pepsine which I tried seemed to contain some albuminous matter which excited Drosera, but the residual grains were not dissolved.—⁴