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Darwin Correspondence Project

From T. L. Brunton   4 September 1874

23 Somerset St. Portman Sq | London W.

Sept. 4th. 1874

My dear Sir

I am sorry that I have been so long in returning an answer to your questions but I asked a friend who was working at urea to make the determinations for me.1 The first method I employed viz to mix urea with glycerine extract of pepsin did not answer as the glycerine disturbed the reaction so much. My friend was therefore obliged after several attempts, to desist—& he shortly afterwards left this country for a holiday excursion   Mr. Wharry a student at St. Bartholomews has been working at the determination of urea since the departure of Mr. West,2 and he has kindly sent me the following analyses which show that the pepsin & hydrochloric acid alone disturb the analyses although glycerine be absent. They make it extremely probable however that urea is not destroyed by digestion. A mixture of equal parts of a solution of urea & of hydrochloric acid of .2 per cent was made pepsin added & the whole well shaken up   It was then divided into equal parts— One half was analyzed for urea at once— It gave 1.7 grammes per 100 cc. nearly the true content. The remainder was warmed to 40oC & left for 48 hours. When analyzed it gave 2.8 grammes per 100 cc. The apparent increase is due to the evaporation of water against which sufficient precautions had not been taken. If any noticeable diminution in the quantity of urea had taken place I do not think this large increase would have occurred.3

I am sorry to say that Dr. Littlejohn’s supply of papaw was all gone when I applied to him some months ago.4 Whenever he gets a new supply he will send me some & I will let you know the result.

I have at last succeeded after

CD annotations

1.8 pepsin … digestion. 1.10] underl blue crayon
1.16 If … occurred. 1.17] scored blue crayon
Top of letter: ‘Digestion’ pencil; ‘Urea | T. Lauder Brunton’ blue crayon


CD was investigating whether urea affected the common sundew, Drosera rotundifolia (see letter to T. L. Brunton, 11 May 1874).
Brunton refers to Samuel Hatch West and Robert Wharry.
Brunton’s results are summarised in Insectivorous plants, p. 124.
On CD’s interest in the juice of the papaw fruit (Carica papaya), see the letter to T. L. Brunton, 25 May [1874] and n. 5. Brunton probably refers to Henry Duncan Littlejohn.


Insectivorous plants. By Charles Darwin. London: John Murray. 1875.


Observations of effect of pepsin and hydrochloric acid on urea indicate that it is not digested [by Drosera].

Letter details

Letter no.
Thomas Lauder Brunton, 1st baronet
Charles Robert Darwin
Sent from
London, Somerset St, 23
Source of text
DAR 58.1: 86–7
Physical description
inc †

Please cite as

Darwin Correspondence Project, “Letter no. 9625,” accessed on 4 June 2023,

Also published in The Correspondence of Charles Darwin, vol. 22