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Darwin Correspondence Project

From J. S. Burdon Sanderson   13 August [1873]1

49, Queen Anne Street. | W.

Aug. 13

My dear Sir,

I regret extremely that I have allowed myself to leave your letter of the 26th of last month so long unanswered.2 It is not so much that I have not had time as that by circumstances my thoughts have been forced to take directions quite away from the subjects which most interest me. Now I am again free.

I am much pleased to learn 1 that drosera digests properly and 2 that it is unable to distinguish between infusions containing albumin of vegetable or animal origin.3

As regards the frog I can reply very definitely to the question “at what temperature are cold blooded animals killed”.

A frog under ordinary circumstances begins to be very much distressed at 85o4 (if immersed in water the temp. of which is gradually raised).

Above 85o up to 95o the distress increases i.e. it makes more & more violent efforts to escape, which efforts eventually assume the convulsive character   Above 95o. the muscles become rigid & the animal dies stiff.

I do not think that the phenomena observed in Drosera when the leaves are heated to 145o. to 150o.5 can be regarded as those of heat rigor. At so high a temperature you come within the range of another kind of change viz that of coagulation of albumin by heat. Albumin coagulates at about 155o, but in presence of acids the temp. of coagulation is always lower, so that I should be inclined to regard the fact that the glands become white and opaque at 145o. as a result of this change.6

The most important facts as regards the physiological action of high tempre. on Drosera, seem to me to be those which prove that within the range of ordinary temp. (i.e. of the temperatures to which the plant is accustomed) the excitability of the glands increases with the temperature   The establishment of these facts seems to be quite sufficient to prove that the relation between the contractile function in Drosera and temperature is the same as in the animal kingdom.

It has occurred to me that it would be very interesting to show that when the Drosera leaf is excited the same electrical changes occur as in muscle & nerve. If you think so, it would not be difficult to plan an experiment.7 The fact if it can be demonstrated, would afford additional evidence of of the identity of the processes.

I am, My dear Mr Darwin | very truly yours | J B Sanderson

CD annotations

1.1 I regret … origin. 2.2] crossed pencil
6.1 I do not … rigor. 6.2] two pencil crosses in margin
7.5 to prove … kingdom. 7.6] scored pencil
8.1 It has … processes. 8.4] crossed pencil
Top of letter: ‘Use | Keep | Heat Rigor’ pencil


The year is established by the relationship between this letter and the letter to J. S. Burdon Sanderson, 25 July 1873.
See letter to J. S. Burdon Sanderson, 25 July 1873. Burdon Sanderson had acknowledged receipt of CD’s letter in his letter of 28 July [1873].
85oF: 30oC.
145–50oF: 63–5oC.
Burdon Sanderson evidently refers to the coagulation temperature of egg albumin (serum albumins coagulate at much higher temperatures). CD cited Burdon Sanderson for information on heat rigor and coagulation in Insectivorous plants, p. 74.
The results of Burdon Sanderson’s initial experiments on electrical phenomena in leaves of Dionaea were reported at the September 1873 meeting of the British Association for the Advancement of Science (Burdon Sanderson 1873a) and given in more detail in the Proceedings of the Royal Society of London (Burdon Sanderson 1873b). His results on the correspondence between animal muscular contraction and the contraction of Dionaea leaves were presented in a lecture at the Royal Institution of Great Britain, 5 June 1874, and published in Nature, 11 June 1874, pp. 105–7, and 18 June 1874, pp. 127–8. CD cited the lecture in Insectivorous plants, p. 318.


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


Answers CD’s questions of 25 July [8987] about temperatures at which cold-blooded animals are killed.

Doubts heat rigor was induced in Drosera. Gives his view of the relation of excitability to increase in temperature.

Suggests experiment to show that electrical changes in plant are the same as in animal muscle and nerve [see Insectivorous plants, p. 318].

Letter details

Letter no.
John Scott Burdon Sanderson, 1st baronet
Charles Robert Darwin
Sent from
London, Queen Anne St, 49
Source of text
DAR 58.1: 34–7
Physical description
ALS 8pp †

Please cite as

Darwin Correspondence Project, “Letter no. 9008,” accessed on 12 September 2023,

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