Ɛpsilon

To F. C. Donders   15 July 1874

Down, Beckenham. | Kent

July 15 74

My dear Prof: Donders,

Your very kind letter has interested me greatly, & it is quite a relief to me to find that such minute doses of atropine act on the muscles & the iris.1 As you remark the eye of a dog is a large object, & the quantity of atropine which acts on each fibre must be as small, or smaller than the quantity of phosphate of Ammonia which acts on a single gland of Drosera. I wish that the quantity of the solution, & therefore of the salt of atropine, which was applied to the eye had been measured; but this perhaps wd. have been useless, as it might have been impossible to ascertain how much was absorbed. Pray thank Pro:. Engelmann for me; I should very much like to see his work, which I cd. return after consulting it, & if he will mark the passages bearing on minute quantities, it would be a great aid, for I read German with much difficulty.2

If Dr. De Ruyter enters into details on the quantity applied I should also like to see his book; but I fear I am very troublesome.3 I shall not return to my M.S. chapter on this subject until one or two months have elapsed.4

With cordial thanks, I remain yours very sincerely, | Charles Darwin

P.S. My son George has just returned worse I fear than when he started.5

Copy

2
Donders had offered to send Theodor Wilhelm Engelmann’s monograph on vibratile movement (T. W. Engelmann 1868) to CD. Engelmann had offered to mark passages that would be useful for CD (see letter from F. C. Donders, 12 July 1874 and n. 10).
3
CD refers to a dissertation written by Donders’s student Gerardus Cornelius Petrus de Ruiter on the action of atropine on the iris (Ruiter 1853; see letter from F. C. Donders, 12 July 1874 and n. 6).
4
In Insectivorous plants, p. 173, CD referred to the amount of sulphate of atropine used by Donders and Ruiter in their experiments; the amount was that mentioned in the letter from F. C. Donders, 12 July 1874.
5
George Howard Darwin had visited Donders in Utrecht, but returned home on 11 July 1874, cutting short his journey after reaching Hanover (Emma Darwin’s diary (DAR 242); letter to J. V. Carus, 9 July [1874]).

Please cite as “DCP-LETT-9547,” in Ɛpsilon: The Charles Darwin Collection accessed on 5 June 2025, https://epsilon.ac.uk/view/dcp-data/letters/DCP-LETT-9547