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Darwin Correspondence Project

To Joseph Fayrer   4 July [1874]1

Down | Beckenham. Kent.

July 4th.

My dear Sir.

Pray forgive my making a small suggestion, if, as I hope you try cobra poison on the white corpuscule, would it not be good for, the control experiment to have the corpuscules in a Sol: of Sugar of the same proportional strength as the cobra poison— I am led to this suggestion from what I have seen with Drosera; & I almost wish that this had been done with the vibratile cilia.—2 The more I think on subject the more surprised I am at different action of the poison on vegetable & animal protoplasm.3

I forgot in my last note to thank you for your offer (if in your power) about Crotalus poison—4 Pray forgive me if you think my suggestion superfluous— I know well that you are a far better judge than I.— If you see Dr. L. Brunton will you tell him I am very curious to hear about the Papaw plant.—5 Also if he has anything more to say about the digestion of pepsine by pepsine & acid;6 but I suppose not.

Yours very faithfully | Ch. Darwin.


The year is established by the relationship between this letter and the letter from Joseph Fayrer, 6 July 1874.
In his letter of 30 June 1874, Fayrer had described an experiment in which he added a solution of cobra venom to some ciliated epithelial cells from the mouth of a frog. As a control, he used cells moistened with water.
In Insectivorous plants, p. 208, CD concluded that though cobra poison was deadly to animals, it was not at all poisonous to Drosera (sundew), but caused strong and rapid inflection of the tentacles.
See letter to T. L. Brunton, 25 May [1874] and n. 5. In his response to CD’s letter of 11 May 1874, Thomas Lauder Brunton had evidently mentioned the digestive properties of the juice of the fruit of the papaw (Carica papaya). Brunton described the digestive action of the ferment papain (derived from pawpaw fruit) in Brunton 1885, pp. 777–8.
Brunton’s earlier comments on the digestion of pepsin may have been made in his response to the letter to T. L. Brunton, 25 May [1874], which has not been found.


Brunton, Thomas Lauder. 1885. A text-book of pharmacology, therapeutics and materia medica; adapted to the United States pharmacopœia. London: Macmillan & Co.

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


Suggests experiment involving cobra poison on white corpuscles. Thanks for offer of Crotalus poison.

Letter details

Letter no.
Charles Robert Darwin
Joseph Fayrer, 1st baronet
Sent from
Source of text
DAR 144: 104
Physical description

Please cite as

Darwin Correspondence Project, “Letter no. 9533,” accessed on 23 October 2020,

Also published in The Correspondence of Charles Darwin, vol. 22