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Darwin Correspondence Project

From John Tyndall   23 February [1871]1

23rd. Feb

My dear Darwin.

I have been recently working at Respirators for firemen, and have devised one which permits a man to remain an hour in smoke, a single inhalation of which, without the respirator, would almost choke him.2

I first tried Cotton-wool; but it let the pungent smoke of resinous pine through freely. A friend then suggested the moistening of the wool with Glycerine. Glycerine had been previously used by Pouchet to make particles stick to a plate of glass.3 I afterwards added fragments of charcoal and hair and in this way have obtained an excellent respirator.

I have had firemen here and they say that they could remain for any length of time in the dense smoke that I had prepared for them.

But what I write to you about is this. The glycerine was a great improvement: even without the coal it does much to quell the most intolerable smoke— it intercepts with extraordinary effect all the floating matter of the air.

Now the human nose with its hairs and mucous is a respirator less perfect than mine, it is true, but still to a great extent effectual.

Supposing a savage tribe to be afflicted with epidemic disease which is undoubtedly propagated by floating particles and that some of them had by a good fortune hairs within their noses: suppose them to breathe through the nose, as many savages to. The chance of survival would certainly any be with those possessing the hairs within the noses. Hairy nosed men would thus be left behind after men without this protection had been cut off. And hence we should have the hairs propagated as we now have them.

I believe this question of hairs within the nose has been a difficulty: but it certainly falls under your general principle.

Yours truly | John Tyndall

Perhaps I am writing about what is already known to you.

CD annotations

Beginning of letter] ‘Use of Hairs in nose’ pencil
End of letter] ‘How is Negro’s nose’ pencil


The year is established by the relationship between this letter and the letter to John Tyndall, 1 March [1871].
Tyndall discussed his work on firemen’s respirators in Tyndall 1871, pp. 334–5, and Tyndall 1874; experiments on them were described in Nature, 7 March 1872, pp. 365–6.
Félix Archimède Pouchet was interested in airborne particles as possible contaminants in experiments that he carried out in order to prove the existence of spontaneous generation (Crellin 1966, DSB).


Has devised a respirator for firemen by moistening cotton wool with glycerine and adding charcoal. JT suggests the nose with its hairs and mucus is a respirator that would give protection against diseases caused by floating particles. The presence of hair and mucus is thus explained by CD’s theory.

Letter details

Letter no.
John Tyndall
Charles Robert Darwin
Sent from
Royal Institution
Source of text
DAR 106: C5–6
Physical description
4pp †

Please cite as

Darwin Correspondence Project, “Letter no. 7508,” accessed on 20 August 2017,

Also published in The Correspondence of Charles Darwin, vol. 19