From J. S. Burdon Sanderson   12 February 1875

Dear M^r. Darwin,

Potassium phosphate is certainly decomposed in the animal body.¹ A double decomposition no doubt takes place between it and common salt which is always present, by virtue of which Potassium chloride & sodium phosphate are produced. It appears to me likely that the reason why potassium phosphate does not act upon Drosera is this—that it is present in considerable proportion in the juices of plants & consequently probably in Drosera.² I think it would be found that to those salts which are present in the plant it is indifferent, even though it may be excited by others which are chemically closely allied to them.

With reference to the subject of experiments on animals, I have after conversation with M^r Huxley prepared a memorandum intended to serve as the basis of a Petition.³ It is now in his hands. I have lately been considering very carefully the whole question and am of course very anxious that if anything is done, it should be done in such a way as to promote rather than to hinder the progress of science.

Believe me, Dear M^r Darwin | Very truly yours | JB Sanderson