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Darwin Correspondence Project

To J. S. Burdon Sanderson   30 April [1876]1

6 Queen Anne St

Sunday— Ap. 30th.

My dear Sanderson

I have read the two papers with the greatest interest.2 It is a grand discovery.

If I understood rightly, you will presently have the machine for enclosing an arm & observing arterial action.3 Should you try any experiments with the machine, & if you think the following one worth trying, I should be particularly glad. It is to test (as suggested by my son Frank) my hyperhypothetical notion on the origin of blushing, namely that thinking intently about any part of the surface of the body tends to relax the arteries in that part.4

You wd probably think of some better scheme than I could; but I may suggest that a man’s arm shd be enclosed & his attention directed intently to his feet; & then that he shd be induced to think as intently as possible about the whole surface of his arm. This might be perhaps best done by some humbug, viz. by asking him to attend to any creeping sensation, or of heat or cold, over the whole surface of the arm, asking him to declare instantly as soon as he felt any such sensation.

Sir H Holland remarked to me long ago, that if you thought intently about any part such as a knuckle or finger, it felt cool as if a breeze were blowing on it, & if my memory does not deceive me, I tried this & found it true..5

Believe me | yours very sincerely | Charles Darwin


The year is established by the address; CD stayed with his brother, Erasmus Alvey Darwin, at 6 Queen Anne Street, London, from 27 April until 3 May 1876 (CD’s ‘Journal’ (Appendix II)).
The papers have not been identified.
Burdon Sanderson adapted the sphygmograph for his work on arterial pulse in the late 1860s (see Frank 1988, pp. 219–23, and Romano 2002, pp. 81–2). His Handbook of the sphygmograph (Burdon Sanderson 1867), included a lecture, ‘On the characters of the arterial pulse’, to the Royal College of Physicians that had previously appeared in parts in the British Medical Journal.
CD presented his theory of blushing in Expression, pp. 310–47. On pp. 338–9, CD hypothesised, attention closely directed to any part of the body tends to interfere with the ordinary and tonic contraction of the small arteries of that part. These vessels, in consequence, become at such times more or less relaxed, and are instantly filled with arterial blood. This tendency will have been much strengthened, if frequent attention has been paid during many generations to the same part, owing to nerve-force readily flowing along accustomed channels, and by the power of inheritance. Francis Darwin did not add any account of experiments that might have been made by Burdon Sanderson to Expression 2d ed.
CD referred to Henry Holland’s observation in his discussions about attention to parts of the body and circulation with other correspondents (see, for instance, Correspondence vol. 19, letter to William Turner, 28 March [1871], and letter to Michael Foster, 16 April 1871). In Expression, pp. 340 n. 35 and 342 n. 42, CD cited Holland 1858, pp. 111 and 92–3, on the effect of consciousness on circulation, and the odd sensations, including cold, experienced in parts of the body that were subjected to conscious attention.


Burdon Sanderson, John Scott. 1867. Handbook of the sphygmograph: being a guide to its use in clinical research; to which is appended a lecture delivered at the Royal College of Physicians on the 29th of March 1867 on the mode and duration of the contraction of the heart in health and disease. London: Robert Hardwicke.

Correspondence: The correspondence of Charles Darwin. Edited by Frederick Burkhardt et al. 29 vols to date. Cambridge: Cambridge University Press. 1985–.

Expression 2d ed.: The expression of the emotions in man and animals. By Charles Darwin. 2d edition. Edited by Francis Darwin. London: John Murray. 1890.

Expression: The expression of the emotions in man and animals. By Charles Darwin. London: John Murray. 1872.

Frank, Robert G., Jr. 1988. The telltale heart: physiological instruments, graphic methods, and clinical hopes, 1854–1914. In The investigative enterprise: experimental physiology in nineteenth-century medicine, edited by William Coleman and Frederic L. Holmes. Berkeley, Calif., and London: University of California Press.

Holland, Henry. 1858. Chapters on mental physiology. 2d edition. London: Longman, Brown, Green, Longmans, & Roberts.

Romano, Terrie M. 2002. Making medicine scientific: John Burdon Sanderson and the culture of Victorian science. Baltimore and London: Johns Hopkins University Press.


Suggests JSBS’s new machine for observing arterial action be used to test CD’s hypothesis that blushing is caused by thinking intensely about a part of the body and thus releasing the arteries.

Please cite as

Darwin Correspondence Project, “Letter no. 10485,” accessed on 30 March 2023,

Also published in The Correspondence of Charles Darwin, vol. 24