From Francis Galton   13 September 1871

My dear Darwin

I had proposed writing to you, in a few days time, about the rabbits when I received y^r. letter.¹ First, let me thank you very much for the kind care you have taken of them. Secondly,— I grieve to hear from you, that your holiday has not been so much of a success as you had hoped. so far as health is concerned² &, thirdly, on my own part, I am glad to say, I am & have been particularly well, (except only a boil inside the ear, which hurt badly for a few days.)

To return to the rabbits:— will you kindly prevent the bucks having any further access to the does, and make away with all the young except, say, 4 or 5 as a reserve in case of continued accident in the forthcoming series of operations.³ As soon as I return to town towards end of October, I will ask you to send me the old rabbits, & will begin at once to cross-circulate every one of them.⁴

My present assistant (a most accomplished young M.B. in medical science) has not the manipulative skill of my old friend & I fear I shall have an undue proportion of corpses, but there must be some successes, out of the 3 does & 3 bucks that you have, & other 3 that I have.⁵

Latterly, my whole heart has been in rats;—white, old English black, & wild grey, which I have had Siamesed together in pairs, chiefly white & wild grey (for my stock of black is low) in a large number of cases—perhaps 30 or 40. pair.⁶ These have been fairly succesful operations so far as the well-beig & comfort of the animals is concerned but unexpected, out-of-the way accidents, are continually occurring. One pair died after 63 (about) days of union and injection into the body of the one passed into the other.

I hope in this way to test Pangenesis better than by the cross circulation for if even 1 drop of blood per hour passes from rat to rat, a volume equal to the entire contents of the circulation of either will be interchanged in 10 days & this is equal in its effects to a pretty complete intermingling of the bloods. All cristalloids diffuse readily from rat to rat (as poison) through the tissues, and as we know that eggs of entozoa are carried through the veins by the blood, it seems that a long continued Siamese union would be a valuable means of experiment.

We look forward with much pleasure on our return to town, to see your daughter in her new home.⁷ I do not think that I wrote myself, for my wife was writing, to offer you which I do now, my heartiest congratulations on the event.—⁸ But, you must miss her.

Ever sincerely your’s | Francis Galton