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Darwin Correspondence Project

To Joseph Fayrer   [1–3 July 1874]1

I dissolved 12 gr. (of cobra-poison)2 in ȝj3 of water, so that I was able to immerse two leaves. It acted as before, but more energetically; and I observed more clearly, this time, that the solution makes the secretion round the glands cloudy, which I have never before observed. But here comes the remarkable point; after an immersion of 48 hours, the protoplasm within the cells incessantly changes form, and I never saw it on any other occasion so active. Hence I cannot doubt that this poison is a stimulant to the protoplasm; and I shall be very curious to find out in your papers whether you have tried its action on the cilia and on the colourless corpuscles of the blood. If the poison does arrest their movement, it will show that there is a profound difference between the protoplasm of animals and of this plant. Therefore if you try any further experiments I hope that you will be so kind as to inform me of the results.4 I may add that I tried at first 1 gr. to the ȝj, as that is my standard strength for all substances.

It is certainly very remarkable that the poison should act so differently on the cilia and on the protoplasm of Drosera.5 After the 48 hours’ immersion, I placed the two leaves in water and they partially reexpanded. I thought that the whitened glands were perhaps killed; but those of one leaf which I tried with carbonate of ammonia absorbed it, and the protoplasm was affected in the usual manner. I am very much surprised at the action of the poison on the viscid secretion from the glands, which it coagulates into threads and bits of membrane, with much granular matter. Have you observed whether the poison affects in any marked manner mucus or other such secretions?


The date is established by the relationship between this letter, the letter from Joseph Fayrer, 30 June 1874, and the letter to Joseph Fayrer, 4 July [1874]. This letter was published in Brunton and Fayrer 1875 (see also letter to Joseph Fayrer, [before 25 June 1874]).
Square brackets in the original: presumably the text was added by Fayrer.
One drachm.
Fayrer had described the results of his experiments on ciliated epithelial cells and the muscle tissues of a frog in his letter of 30 June 1874.
In Fayrer’s experiment, the ciliae ceased all movement within minutes (see letter from Joseph Fayrer, 30 June 1874). CD’s experiment was performed on Drosera rotundifolia, the common or round-leaved sundew (see Insectivorous plants, pp. 206–8).


Cobra poison is a stimulant to protoplasm. Poison acts very differently on cilia and protoplasm of Drosera.

Letter details

Letter no.
Charles Robert Darwin
Joseph Fayrer, 1st baronet
Source of text
Proceedings of the Royal Society of London 23 (1874–5): 274

Please cite as

Darwin Correspondence Project, “Letter no. 9527F,” accessed on 20 June 2019,

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