Ɛpsilon

To F. J. Cohn   3 January 1878

Down, | Beckenham, Kent.

Jan 3. 1878.

My dear Sir.

I thank you sincerely for your most kind letter & I return your wishes for the new year with all my heart.1 Your letter has interested me greatly. Dr Sanderson showed me some admirable photographs on glass by Dr Koch of the organisms which cause splenic fever; but your letter & the valuable work which you have kindly given me make the case much clearer to me.2 I well remember saying to myself, between 20 & 30 years ago, that if ever the origin of any infectious disease could be proved, it would be the greatest triumph to science; & now I rejoice to have seen this triumph.

With respect to the filaments of Dipsacus, I do not for a minute put my judgement on a par with yours or that of de Bary, but my son has lately made some observations which incline me very strongly to believe that the filaments consist of living matter of the nature of protoplasm3   Hearing from Dr Sanderson that thymol has a fatal effect on low organisms, he tried solutions of 110% & 120% both of which cause contraction of the filaments. On the other hand 12% solution of carbolic acid does not cause contraction, 1% does so, this agrees with several observers who find, I believe, that 12% carbolic solution is not poisonous to microzymes. My son finds that strong solutions of NaCl cause contraction but not death, as the filaments recover themselves in water, & do not swell up into bladders as they do after poisons; this agrees with H. de Vries’ work on the ‘plasmolysis’ of cells—4

With cordial thanks & much respect | I remain, my dear Sir | Yours sincerely | Charles Darwin

LS

1
See Correspondence vol. 25, letter from F. J. Cohn, 31 December 1877.
2
Cohn had sent CD the third and last issue of the second volume of Beiträge zur Biologie der Pflanzen (Contributions to the biology of plants), a journal that he edited. It contained an article by Robert Koch, ‘Verfahren zur Untersuchung, zum Conserviren und Photographiren der Bacterien’ (Method for examining, preserving and photographing bacteria; Koch 1877). It is not known when John Scott Burdon Sanderson showed CD Koch’s photographs; he had met Koch in Germany and assisted with an experiment in October 1877 (Correspondence vol. 25, letter from F. J. Cohn, 31 December 1877), and he reproduced figures from some of Koch’s photographs in his ‘Lectures on the infective processes of disease’ (Burdon Sanderson 1877–8; for the figures, see British Medical Journal, 9 February 1878, p. 181). Splenic or splenetic fever is now known as anthrax.
3
In his letter of 31 December 1877, Cohn had critiqued Francis Darwin’s paper ‘On the protrusion of protoplasmic filaments from the glandular hairs on the leaves of the common teasel (Dipsacus sylvestris)’ (F. Darwin 1877b), mentioning apparently similar phenomena observed by Anton de Bary in Agaricus (a genus of mushrooms).
4
Francis Darwin published the results of his experiments on Amanita agaricus (fly agaric) and Dipsacus sylvestris (common teasel) in F. Darwin 1878b; he concluded that the effect of salt and acid solutions on the filaments suggested that the filaments contained living matter, and that their contraction was not merely mechanical. He cited Hugo de Vries’s work on the mechanical expansion and contraction of cells (Vries 1877a and 1877b). See Vries 1877a, p. 4, for his use of the term plasmolysis for the shrinking of protoplasm from the cell wall. Microzyme: bacterium. NaCl: sodium chloride.

Please cite as “DCP-LETT-11310,” in Ɛpsilon: The Charles Darwin Collection accessed on 5 June 2025, https://epsilon.ac.uk/view/dcp-data/letters/DCP-LETT-11310