To T. L. Brunton 11 May 1874
Down, | Beckenham, Kent.
May 11 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 10m. After from 6h.— to 8h 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
Footnotes
Bibliography
Insectivorous plants. By Charles Darwin. London: John Murray. 1875.
Summary
Encloses, for examination, residue from skim-milk which has been on the glands of Drosera. Asks TLB to confirm his views on action of Drosera secretion on milk. Asks about effects of pepsin and hydrochloric acid in digestive juice.
Letter details
- Letter no.
- DCP-LETT-9453
- From
- Charles Robert Darwin
- To
- Thomas Lauder Brunton, 1st baronet
- Sent from
- Down
- Source of text
- Princeton University Library, Department of Rare Books and Special Collections, Manuscripts Division (C0140 Box 13 AM20431)
- Physical description
- LS(A) 4pp
Please cite as
Darwin Correspondence Project, “Letter no. 9453,” accessed on 24 April 2024, https://www.darwinproject.ac.uk/letter/?docId=letters/DCP-LETT-9453.xml
Also published in The Correspondence of Charles Darwin, vol. 22