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From William Roberts   30 June 1877

89 Mosley St. | Manchester

June 30/77

Dear Sir,

Will you pardon me troubling you with a brief inquiry?. I have been appointed to read the address in Medicine at the approaching meeting of the British Medical Association—to be held in Manchester in the beginning of August.1

My subject is the parasitic nature of infective & contagious diseases. I propose to develop the idea that pathogenic organisms are variations of some common bacterium of similar morphology—that the Bacillus anthracis for example (the organism of Splenic fever) is a parasitic variation of the Bacillus Subtilis.2 And the question I wish to ask you is this:— do you know of any animal or plant which has varied in this way—i.e. has acquired the parasitic habit.—or can you refer me to any source of information on the subject. I have been looking over your volumes on “the variation of plants & animals under domestication” without finding what I want.3 My excuse for troubling you is the great pressure on my time—and the short period between this and the 7th of August.

I hope you will pardon my intrusion on your valuable leisure.

Believe me | yours faithfully | Wm. Roberts

C. Darwin Esq F.R.S. etc

1
Roberts’s address was given to the forty-fifth annual meeting of the British Medical Association, held at Owens College, Manchester, where Roberts was professor of clinical medicine. A copy of the paper (Roberts 1877) is in the Darwin Pamphlet Collection–CUL.
2
Bacillus subtilis, also known as hay or grass bacillus, is a normally harmless bacterium found in soil and the gastrointestinal tract of ruminants and humans. Bacillus anthracis had been recently identified as the agent of anthrax (or splenetic fever) by Robert Koch (R. Koch 1876). Roberts discussed microscopical work by Koch and Ferdinand Julius Cohn, which showed developmental and morphological similarities between the two bacilli (Roberts 1877, pp. 35–8).
3
Roberts cited cases of bud variation described by CD in Variation 1: 340, and suggested that Bacillus anthracis had evolved as a sport of Bacillus subtilis (Roberts 1877, pp. 38–9).

Please cite as “DCP-LETT-11025,” in Ɛpsilon: The Charles Darwin Collection accessed on 5 June 2025, https://epsilon.ac.uk/view/dcp-data/letters/DCP-LETT-11025