3 1 4 D O C . 3 7 5 A P R I L 1 9 2 0 the function of an inbred trait that counts. This influence, at the very least, could not be dismissed and considering that other experiments (Johannsen, who is cer- tainly impartial on this point, because he is one of the bitterest opponents of the the- ory of heredity of acquired characteristics),[2] and Mendelism as a whole, prove that selection is thoroughly ineffective as a creative factor, acting rather only as a factor of elimination and dissemination consequently, only living conditions and the functional environment remain. This is clear from the breeding of thoroughbred horses and quality dairy-cows: because the fastest racers are not simply selected out, but their abilities are tested as well and they are given plenty of occasion to run one doesn’t just choose cows or heifers from good milking stock, but one milks them to full advantage otherwise, one evidently would not be in a position to es- tablish such a crucial trait. The best book on the heredity of acquired traits is by Richard Semon, Das Prob- lem der V[ererbung] erw[orbener] Eig[enschaften], Leipzig Engelmann, 1912.[3] My results are emphasized and critically reviewed there too, and are even com- pared against my opponents’ objections. In a slightly later mailing I am going to send you a few more recent papers that have since appeared.[4] Do still allow me to make a request: recently at Popper-Lynkeus’s I saw a fine photograph of you with a dedication.[5] I would be exceedingly grateful if you would send me one like it or similar to it. I hope your daughter has my last, long letter, which, it seems to me, traveled to Berlin exactly during the last revolutionary upheavals and constituted an answer to your letter. With utmost respect, yours very truly, Dr. Paul Kammerer. 375. From Paul Ehrenfest [Leyden,] 16 April 1920 Dear Einstein, You did, I hope, receive 1st my letter 2nd, the two inaugural speeches.—[1] To- day Onnes wrote to the Minister authorizing the Dutch consulate (not embassy!) in Berlin to issue you a Dutch visa as soon as you apply for it—[2] so please start with that directly, so that you can come soon.– I thank Miss X. Einstein (name totally illegible) very sincerely for the detailed information about your curriculum vitae.[3] She did such a wonderful job of it that I shall soon avail myself of her kindness again. Bring photographs along so that for once a better picture can be made of the