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Darwin Correspondence Project

To Joseph Fayrer   [before 25 June 1874]1

You will perhaps like to hear how it acted on Drosera. I made a solution of 14 gr. to ȝij of water.2 A minute drop on a small pin’s head acted powerfully on several glands, more powerfully than the fresh poison from an adder’s fang.

I also immersed three leaves in 90 minims of the solution; the tentacles soon became inflated and the glands quite white, as if they had been placed in boiling water. I felt sure that the leaves were killed; but after 8 hours’ immersion they were placed in water, and after about 48 hours reexpanded, showing that they were by no means killed. The most surprising circumstance is, that, after an immersion of 48 hours, the protoplasm in the cells was in unusually active movement. Now, can you inform me whether this poison, if diluted, arrests the movement of vibratile cilia?3

I dissolved 12 gr. (of cobra poison)4 in ȝj 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. 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. 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 mush 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 and the letter from Joseph Fayrer, 25 June 1874.
Fayrer had enclosed a small quantity of cobra poison with his letter of 17 June 1874 for CD’s experiments on Drosera (sundew). ȝ: dram (one-eighth of an ounce); j: i, one (Roman numeral). ȝij: two drams.
Vibratile or motile cilia are hair-like organelles that extend from the surface of cells in animals and have a waving motion.
‘(of cobra poison)’: square brackets in printed source; presumably an editorial insertion by Fayrer.


Fayrer, Joseph. 1875. The royal tiger of Bengal, his life and death. London: J. & A. Churchill.


Sends observations of poison acting on glands of Drosera. Poison acts as a stimulant to protoplasm. Very remarkable that poison acts so differently on the 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): 273–4
Physical description

Please cite as

Darwin Correspondence Project, “Letter no. 9512F,” accessed on 20 September 2020,

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