To Charles Buxton   12 October [1864]¹

My dear Sir

I trust to your kindness to excuse me for troubling you with a question. I received a message from Sir H Holland that he was told that at your brewery “they cannot go on with their own yeast but are obliged to interchange with other breweries”.² Is this a fact or a prejudice?³

The point interests me much; more especially as the yeast does not propagate sexually   I should be very much obliged if you could give me any reliable information on this head, & permit me to quote you as my authority.

I add a few questions as some sort of guide for information.

Pray believe me my dear Sir | yours sincerely | Charles Darwin

Any time when convenient for you to answer would perfectly suit me.— 1. How long will yeast, from being first introduced into your brewery, last good? 2. In what way does it fail? 3. Will yeast from any other brewery serve your purpose? 4. When your own yeast has ceased to be good, will it act if used in any other brewery? 5. And conversely will yeast which has become worn out in some other brewery, do for you? 6. In short does the yeast simply require a change of any kind, or, as it w^d be said with a convalescent, a change of air?