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Darwin Correspondence Project

To J. S. Burdon Sanderson   14 September [1873]1

Down, | Beckenham, Kent.

September 14th.

My dear Dr. Sanderson

I have been extremely glad to hear what Frank has told me, and I am very much obliged to you for having allowed him to aid you.2 It seems a fine discovery, and I should think would lead to much further research; I am very glad that you are going to report on it to the Brit. Assoc.3

Thanks for the paper which I will keep for a week or two, as I find I have only the second part.4

And now I am going to beg a favour of you which I stand in great need of. viz a small quantity of a few pure animal substances, namely fibrin, albumin, mucin,5 or any others which are tolerably distinct. Perhaps you could persuade Dr Brunton6 to aid me in this; of fibrin I want nearly a drachm for a distinct & special purpose but of other substances much less; the fibrin must be absolutely pure of all salts for the special purpose in view i.e. to excite acid secretion & get the acid ascertained.— Frankland is away, Miller is dead, and Hoffmann at Berlin and I now know no one else to whom to apply.7 Do you know any professional chemist whom I could pay and who could be trusted to prepare such substances pure? The reason of my wanting these substances is, that I fine absolutely pure gelatin formerly given me by Hoffmann, does not cause Drosera to be inflected, though isinglass does.8 Again as far as I have gone (though my experiments are not completed) neither casein nor glutin (from wheat-flour)9 affects drosera. As meat of all kinds, dead insects of all kinds, and white of egg all act most energetically, I am very curious to know—what pure animal compounds will act. It seems even possible !!! that this subject might throw a little light on animal digestion, for I see old Müller suspects that something more than gastric juice is required to digest certain animal substances.10

Yours very sincerely | Ch. Darwin


The year is established by the relationship between this letter and the letter to J. S. Burdon Sanderson, 13 September [1873].
Francis Darwin was a medical student at St George’s Hospital, London; he evidently assisted Burdon Sanderson in his research on Dionaea muscipula (Venus fly trap), which was carried out in the laboratory of University College London.
For the summary of Burdon Sanderson’s presentation to the meeting of the British Association for the Advancement of Science, see Burdon Sanderson 1873a. The meeting was held at Bradford from 17 to 24 September 1873 (Report of the 43rd meeting of the British Association for the Advancement of Science, held at Bradford (1873), p. lxix).
The paper has not been identified.
Albumin is a class of water soluble proteins found in animal and plant tissues. Mucin is a class of glycoproteins (proteins with an attached carbohydrate). Fibrin is an insoluble protein essential for blood clotting. Its digestibility had been reported in Klein et al. 1873, 1: 486–7.
Edward Frankland was in Switzerland (see letter from Edward Frankland, 17 July 1873). August Wilhelm von Hofmann, his predecessor at the Royal College of Chemistry, was professor of chemistry at Berlin. William Allen Miller had died in 1870 (ODNB).
In 1862, Hofmann had supplied thin sheets of gelatine free from contamination by chlorine for some of CD’s early experimental work with Drosera (sundew; see Correspondence vol. 10, letter from A. W. von Hofmann, 27 June 1862, and Insectivorous plants, pp. 110–11). Both gelatine and isinglass are forms of collagen, the former usually derived from skin, bones, and other tissues of mammals, while the latter is from the swim-bladders of fish.
Casein and gluten are similar proteins; the former is derived from milk, while the latter is found in grains from the grass family (Poaceae).
Johannes Peter Müller and Theodor Schwann published their results on artificial digestion in 1846, noting that acid alone left cubes of albumen (egg white) unchanged while those treated with extract of stomach lining showed visible changes after twelve hours (Müller and Schwann 1836, p. 68). They concluded that digestion of substances containing protein required not only an acid environment but also an unknown chemical substance (Princip; ibid., p. 86). Schwann later isolated pepsin, the first digestive enzyme to be discovered (NDB).


Correspondence: The correspondence of Charles Darwin. Edited by Frederick Burkhardt et al. 29 vols to date. Cambridge: Cambridge University Press. 1985–.

Insectivorous plants. By Charles Darwin. London: John Murray. 1875.

NDB: Neue deutsche Biographie. Under the auspices of the Historical Commission of the Bavarian Academy of Sciences. 27 vols. (A–Wettiner) to date. Berlin: Duncker & Humblot. 1953–.

ODNB: Oxford dictionary of national biography: from the earliest times to the year 2000. (Revised edition.) Edited by H. C. G. Matthew and Brian Harrison. 60 vols. and index. Oxford: Oxford University Press. 2004.


Very pleased at JSBS’s discovery ["On the electrical phenomena which accompany the contractions of the leaf of Dionaea muscipula", Rep. BAAS 43 (1873): 133].

Asks for pure animal substances [proteins] for Drosera experiments. His other sources have been T. L. Brunton, Edward Frankland, W. A. Miller (now dead), and Hoffmann of Berlin [A. W. von Hofmann?].

Please cite as

Darwin Correspondence Project, “Letter no. 9056,” accessed on 29 May 2023,

Also published in The Correspondence of Charles Darwin, vol. 21