His scientific achievements aside, Kuhn’s opportunistic behaviour during the Nazi regime in Germany has been and still is a controversial subject. In 2005 the German Chemical Society decided to abolish the Richard-Kuhn-Medal, because it saw its name-patron unsuited as a role model. The medal had been awarded to excellent international biochemists since 1968. In a letter to the society’s Journal, 1981 Chemistry Laureate Roald Hoffmann, who lost most of his family in the holocaust, commended this decision, stating: “He was a great scientist, but no example for German chemists.” .
In the present lecture, Kuhn talks about one of his major fields of interest: vitamins and other bioactive substances found in milk. He briefly covers the carotenes (which represent different chemical forms of vitamin A and are responsible for the slightly yellowish colour of fresh milk) and riboflavin (vitamin B2). His work in this field was awarded with the 1938 Nobel Prize in Chemistry. The major part of the present talk, however, is reserved for investigations with respect to the metabolism of bifidobacteria. Bifidobacteria play an important role in the function of the mammalian colon and have hence appeared as beneficial food additives in yoghurts and related products in recent years. Kuhn lectures with great detail and clarity on experiments with a special variety of bifidobacteria (a mutant), which grows on human milk but not on cow’s milk. The discovery of this mutant by Paul György’s group, who had also discovered vitamin B6 in 1934, was a small sensation, because it implied that there is a yet unknown nutritional difference between the two milk types. This appeared to be of particular relevance, as around the middle of the 20th century, women increasingly used baby formula mixed with cow’s milk instead of breast feeding their children. It was thus Kuhn’s aim to identify the individual chemical constituent that made human milk support the growth of the mutant bifidobacteria, i.e. the so-called growth factor. Most of the experiments described were done in collaboration with Paul György and, only a few years after Kuhn’s talk, György’s group and others showed, that not one but several growth factors for the mutant bifidobacteria existed in human milk. Still, the nowadays well-known fact that cow’s milk is unsuited for feeding babies, is not due to the lack of these growth factors but to the lack of certain vitamins and an unfavourable protein content.
Kuhn closes his talk by pointing out that the research on the bifidus growth factor is an excellent example of the increasing importance of microbiology in the research on vitamins and other bioactive substances. By using relatively easy-to-handle bacterial cells instead of entire animals, studies of bioactivity could be speeded up massively. From a modern point of view, Kuhn’s judgement on the importance of microbiological methods was absolutely correct. In fact, around the time of the talk, scientists in the United States for the first time succeeded in growing human cells in a petri dish. These so called HeLa cells were shipped to laboratories all over the world and formed the basis for a wide array of bioactivity studies and biological work, which had a massive impact on 20th century medicine.
Correspondence of members following the decision of the society can be found in Nachrichten aus der Chemie 2006, pages 54, 495, 510 and 573.