D O C U M E N T 3 4 4 S E P T E M B E R 1 9 2 2 4 9 5 344. From Jacques Loeb The Rockefeller Institute for Medical Research, New York 66th Street and Avenue A Marine Laboratory, Woods Hole, Mass. September 4, 1922 My dear Professor Einstein: It was extremely kind of you to take the trouble of reading my book and to write to me in such an appreciative way.[1] The reason why the protein molecule only acts as acid or as base is difficult to explain, except that it is a fact as far as gelatin and proteins in general are concerned. I have ventured to explain it in analogy with the experiences on indicators which have shown that the chromophore group of indi- cators undergoes a tautomeric change at a definite hydrogen ion concentration. As a preliminary suggestion, I offered the idea that an isomeric change may also occur in the protein molecule at a critical hydrogen ion concentration. We were all very much worried and shocked at the turn of events in Germany. I think it is an excellent idea for you to follow the invitation which takes you across the seas, and I only wish that you would accept my suggestion that I made to you a year ago, that you spend several years in the United States. If you would consider this possibility, I think arrangements could be made whereby you could have full independence and facilities to work. I do not think that matters will be very much different in Germany in the next few years. Will you let me know how you feel about this matter? I have had to abandon my trip to Germany for the reason that Mrs. Loeb was not very well and that it looked for a time as if she had to undergo a serious operation. I could not make up my mind to go to Germany with the burden of that worry re- sting on my shoulders, and it seemed only fair to me that I should inform the com- mittee of this situation. It would have been a great satisfaction to me if I had had a chance to bring some of my results before the physical chemists, since I have a very limited audience in this country and since in Germany they are not familiar with the literature published during the year.[2] In addition, the opposition on the part of the majority of the biologists to any application of physical chemistry to biological problems, and the opposition of the old-fashioned type of colloid chemists like Wolfgang Ostwald, prevent the dissemination of these facts in German literature. I hope it will be possible, finally, to get support in this country for those German scientists who are able to do the right kind of work if not, I am afraid there will be added to the brutality following this war the cessation of scientific activity which can only result in keeping the forces of brutality longer in power. I remain with kindest regards from all of us to yourself and Mrs. Einstein, Yours very sincerely, Jacques Loeb