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Darwin Correspondence Project

From F. J. Cohn   31 December 1877

Breslau, | Schweidnitzer Stadtgraben 26.

den 31ten. December 1877

My dear Sir

The approaching new-year remembers me of the great philosopher who devoting his leisure with incomparable assiduity and success to the promotion of science, embraces the humblest of his fellow-students with the kindness of his sympathy. I beg to send to you my best wishes for new year and many happy returns of this day.

I take the liberty of sending the last part of my “Beiträge zur Biologie der Pflanzen, which contains the first photograms of Bacteria, executed by my friend Dr. Koch.1 Though we hope, to obtain still better results, the plates in question afford, however, excellent proofs of copies of the least but also perhaps the mightiest living beings, made with the exclusion of any subjective or personal error. I beg to direct your attention to Fig 8 plate XV. Micrococcus, the smallest and simplest of all organisms, to the flagella of Spirillum and Bacillus Plate XIV fig. 4, 5, 6, to fig 1 of the same plate, which represents a stream or cumulus of Bacteria under lower power, which like a nebula of stars dissolves under high power (fig 2) in swarms of Bacteria, and mostly to Plate XVI where you find photogramms of the most important pathogenic Bacteria (fig. 7 and 8 Spirochaete of febris recurrens—and fig 1–5 Bacillus Anthracis of Splenic fever.)2 The copies of the former species are obtained from drops of blood of sick people in a St. Petersburgh Hospital, dried upon small glass plates; and soaked and prepared in Breslau after Dr. Koch’s method.3 The history of these spiral motile filaments is still obscure; but the history of Bacillus Anthracis and its importance in producing splenic fever, is disclosed with admirable penetration by Dr. Koch.4 You will remark the spores originating in the articles of the filaments, which resist exsiccation after the destruction of the filaments themselves, and remain capable of multiplying and germinating and then producing sickness and death many years. Last October we had the pleasure to enjoy of Dr. and Mrs Sandersons5 presence as dear guests in our house, and then Dr. Koch was able under his attendance to inoculate splenic fever into rabbits with an extremily small quantity of blood, taken out of the spleen of a cow, five years before, and dried since that long time; all the rabbits died after two–three days, and their liver, spleen and blood showed full of living Bacillus, grown out of the spores inoculated with the dried blood.

The small paper on Dipsacus is a very incomplete abstract of a lecture delivered in the Botanical Section of the Meeting of German naturalists in Munchen in Sept. last. I hoped to agree with your wishes by producing before that forum the highly interesting discoveries of your son, M. Francis D. By repeating his observations, I was at first extremely struck by the impression of those curious filaments, protruding, undulating and retiring in the most extraordinary way.6 But after maturer reflection, I am convinced that there is no living phenomenon, but that some substance secreted by the glands between their cells and the cuticule, and swelling in water, is protruded through vents in the cuticle; the apparition remembers me of certain toys which were very common some years ago in Germany and perhaps also in England; they were called “serpents de Pharaon” and consisted of some compound of mercure, which when kindled, grew into very long serpentile, burning and rotating filaments.7 The retraction of the filaments of Dipsacus seems to me caused by withdrawing water from the gland-cells through endosmotic reagents.

The study of the former observations on the filaments of Agaricus published by De Bary2 and Hoffmann1, which wholy agree with those of Dipsacus, seems to me to support with high probability the supposition that we have to deal in both cases with an endosmotic phenomenon, not with such one of true life.8 De Bary himself explained after my lecture his researches on the vibratile filaments of Agaricus which he had enquired into, 15 years before, and had found soluble in Alcohol; your son himself has made the same discovery in Dipsacus, which had puzzled him very much.9

I have read since the paper of Virchow on Myeline (Virchows Archiv 1854) a substance he pointed out in the marrow of nerve fibres, brain, spinal marrow, in spleen, lungs, blood, pus, yolk etc; the external appearance, the movements and transformations of myeline, for ought I saw, are not very like the filaments of Dipsacus, but they agree in their solubility in Alcohol and in soaking and swelling in water.10 The whole question however is still so very curious and so much enveloped in obscurity, that your son, by directing through his discovery the attention upon this neglected object, has very well deserved of science.

May the coming new year afford to you all reward science and philosophy can bestow upon their first promotor, and may yourself and your family be blessed in body and mind. | Truly yours | Ferdinand Cohn


CD’s copy of Beiträge zur Biologie der Pflanzen, vol. 2, part 3 has not been found. The article by Robert Koch, ‘Verfahren zur Untersuchung, zum Conservieren und Photographieren der Bacterien’ (Method for research into preservation and photographing of bacteria; R. Koch 1877) included three plates made directly from Koch’s photograms using the method he devised himself and outlined in his paper.
Micrococcus is a genus in the family Micrococcaceae; Bacillus is in the family Bacillaceae; both are in the subkingdom Posibacteria. These genera were first identified by Cohn in 1872 (Cohn 1872). Spirillum is a genus of Negibacteria in the family Spirillaceae. Febris recurrens: recurring fever (Latin), an alternative name for typhoid fever. Bacillus anthracis is the bacteria that causes anthrax; splenic fever was another name for the disease.
Koch’s method was described in his article ‘Die Aetiologie der Milzbrand-Krankheit, begründet auf die Entwicklungsgeschichte des Bacillus Anthracis’ (The aetiology of anthrax-sickness, based on the developmental history of Bacillus anthracis; R. Koch 1876).
An abstract of Cohn’s paper ‘Ueber vibrirende Fäden in den Drüsenhaaren von Dipsacus’ (On the vibratile filaments in the glandular hairs of Dipsacus; Cohn 1877b), delivered on 21 September 1877 at the meeting of German naturalists and doctors in Munich, was published in the Amtlicher Bericht der 50 Versammlung Deutscher Naturforscher und Aertze. In August 1877, Cohn had repeated some of Francis Darwin’s experiments on the protrusion of protoplasmic filaments from glandular hairs in the cups formed by leaves of common teasel (Dipsacus sylvestris, a synonym of D. fullonum); CD had sent Cohn’s results, confirming many of Francis’s observations, to Nature (see letters from F. J. Cohn, 5 August 1877 and [10?] August 1877, and letter to Nature, 15 August [1877]).
When mercury thiocyanate (Hg (SCN)2) powder is ignited it rapidly produces a coiling snake-like solid, which is called Pharaoh’s serpent; the reaction was discovered in 1821 by Friedrich Wöhler and the substance was available as a novelty item until its toxicity was discovered (T. L. Davis 1940).
Anton de Bary discussed the structure and movement of filaments of Agaricus in Bary 1859, pp. 386–7. Hermann Hoffmann discussed contractile bodies in gilled mushrooms in Hoffmann 1853 (see letter to F. J. Cohn, 8 August 1877 and n. 3). Agaricus is a genus of mushrooms in the family Agaricaceae. ‘1’ and ‘2’, added later, are presumably a reference to the order of publication.
Francis Darwin described the effects of adding alcohol to the filaments of teasel in F. Darwin 1877b, pp. 252–3.
Rudolf Carl Virchow had given the name ‘myelin’ to the organic compound that formed the insulating layer around nerve fibres and was also found in other tissues (Virchow 1854, p. 571). He extracted myelin from pus using alcohol and added water to the extract, noting that the movement of the hydrated substance sometimes led to its forming numerous filiform branches (ibid., pp. 570–1).


Bary, Anton de. 1859. Zur Kenntniss einiger Agaricinen. Botanische Zeitung 17: 385–8, 393–8, 401–4.

Davis, Tenney L. 1940. Pyrotechnic snakes. Journal of Chemical Education 17: 268–70.

Hoffmann, Hermann. 1853. Ueber contractile Gebilde bei Blätterschwämmen. Botanische Zeitung 11: 857–66.

Koch, Robert. 1876. Untersuchungen über Bacterien. V. Die Aetiologie der Milzbrand-Krankheit, begründet auf die Entwicklungsgeschichte des Bacillus Anthracis. Beiträge zur Biologie der Pflanzen 2 (1876–7): 277–310.

Koch, Robert. 1877. Verfahren zur Untersuchung, zum Conserviren und Photographiren der Bacterien. Beiträge zur Biologie der Pflanzen 2 (1876–7): 399–434.

Virchow, Rudolf. 1854. Ueber das ausgebreitete Vorkommen einer dem Nervenmark analogen Substanz in den thierischen Geweben. Archiv für pathologische Anatomie und Physiologie und für klinische Medicin 6: 562–72.


Sends details of H. H. R. Koch’s work on bacteria, including first photographs.

J. S. Burdon Sanderson’s and Koch’s collaboration on systemic fever.

Thinks movement of Francis Darwin’s Dipsacus filaments is an artifact.

Letter details

Letter no.
Ferdinand Julius Cohn
Charles Robert Darwin
Sent from
Source of text
DAR 161: 205
Physical description
ALS 6pp

Please cite as

Darwin Correspondence Project, “Letter no. 11298,” accessed on 1 October 2023,