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Darwin Correspondence Project

From Michael Foster   [26 June 1871]1


Monday Ev.

My dear Sir

I have written to my man at Cambridge to send you by post a bottle of urari of which please use as much as you want—& when you have quite done with it I will have the remainder back.2 I have two stocks—one Sharpey3 gave me—gathered by Dr. Dalton,4—the other purchased in Leipzig— I don’t know which will reach you because I don’t quite know which my man will lay his hands upon.

As to doze I hardly know what to say— Urari does not neutralize strychnia but prevents the muscular manifestations of the action of strychnia— Hence any dose sufficient to paralyse completely the motor nerves (and for a frog I generally take a drop of two of a solution made by mixing thus much 0 in about 3j5 of water) will negative the action of almost any qty of strychnia great or small. The urari is eliminated slowly so that by the time the action of even a small dose of urari is passing off, the effect of a large dose of strychnia has also passed away.6

I think I am right in saying that in the absence of histologically distinct nervous elements urari seems inert— ex gr.7 amoebae go their ways as usual in even strong solutions of it—& protoplasm generally seems to be unaffected by it— I believe these are Kühne’s results.8

It is extremely soluble in cold water—& the clear filtrate possesses all the virtues.

Believe me | Yours ever truly | M. Foster

CD annotations

3.1 I think … inert— 3.2] triple scored red crayon
Top of letter: ‘Keep | Drosera’9ink


The date is established by the relationship between this letter and the letters to Michael Foster, 26 June [1871] and 29 [June 1871]. In 1871, 26 June was a Monday.
See letter to Michael Foster, 26 June [1871] and n. 3. Urari is an alternative name for curare. Foster’s assistant has not been identified.
William Sharpey.
Dr Dalton has not been identified.
[dram]: dram, one sixteenth of an ounce. j: i, one (Roman numeral).
See letter to Michael Foster, 26 June [1871] and n. 4. ‘Strychnia’ is a synonym of strychnine. Curare blocks the transmission of nerve impulses at the neuromuscular junction in animals, resulting in paralysis, while strychnine has a stimulant effect and causes convulsions.
Ex. gr.: exempli gratia (for instance).
Foster refers to Wilhelm Friedrich Kühne and Kühne 1860.
CD used curare (urari) in experiments on Drosera rotundifolia (see letter to Michael Foster, 26 June [1871] and n. 4).


Kühne, Wilhelm Friedrich. 1860. Ueber die Wirkung des amerikanischen Pfeilgiftes. Archiv für Anatomie, Physiologie und wissenschaftliche Medicin 1860: 477–517.


Has arranged to send CD a bottle of urari [curare]. Describes its effect with strychnine.

Letter details

Letter no.
Michael Foster
Charles Robert Darwin
Sent from
Source of text
DAR 58.1: 141–2
Physical description
4pp †

Please cite as

Darwin Correspondence Project, “Letter no. 7834,” accessed on 30 September 2020,

Also published in The Correspondence of Charles Darwin, vol. 19