On Hamburger's review of Holtfreter's manuscript. On theories about induction: "I find that all this kind of speculating, including my own stuff on proteins, is rather cheap. I did it only because I thought it to be a little bit more fitting than what I had read about induction, especially in Waddington's revelations. Anybody today who takes the risk of interpreting induction in general terms is bound to be caught as a blunderer. I find that all these theories of Waddington, Dalcq, Barth etc. are not much else than a hitting upon an analogy and the attempt to elaborate upon it. Some of them sound a bit more pleasant, others less so, but all are 99% poetry. Harrison and Spemann were wise enough never to go far along the slippery road of speculations but they were nevertheless kept going by the phantasmagorias of Driesch [,] Weismann, Roux and the like. Anyway, persons who emit their theories abut induction should follow them up experimentally as far a[s] possible, otherwise they are just annoying."Handwritten. Has note by Hamburger on first page: "Barth induction 99% poetry".3-page letter