The production of diabetes after total pancreatectomy in the dog by von Mering and Minkowski was one of the greatest advances of the experimental medicine, that demostrated the internal secretion of the pancreas and led to the discovery of insulin. Diabetes was an unexpected finding in the course of experiments planned for the study of the intestinal absorption of fats. The hazard favored men well prepared, that were active in diabetic research. The real history of the events was unknown until recently and a lot of fantastic stories were widespread. The present publication of a personal letter of Minkowski, in German, accompanied by the Spanish translation (the English translation appeared in Diabetes, 1952, 1, 112-116, but not the german text), explains clearly the truth abouth these facts.