Sir

Although the discovery of nucleic acids, mentioned in Peter Little's News and Views article (“The book of genes” Nature 402, 467; 1999), was published in 1871, the Swiss physiologist Johann Friedrich Miescher (1844–95) actually made the discovery two years earlier.

Working in Tübingen between autumn 1868 and 1869, Miescher isolated the new substance from cells of pus (leukocytes) obtained from discarded bandages from the local surgical clinic. In order to find the chemical constitution of nuclei, he removed the proteinaceous cytoplasmic substances of the cells by digestion with gastric juice (containing the protease pepsin) from pigs' stomachs and with hydrochloric acid. The material of the naked nuclei that he obtained and called “nuclein” contained 14 per cent nitrogen, 2 per cent sulphur and 6 per cent phosphorus pentoxide, making it very rich in phosphorus.

The final studies were made in the autumn of 1869, because on 21 August that year Miescher wrote to his parents: “I still have to complete the definitive analysis of the nuclear substances.” And the paper is dated “Basel, October 1869”. Miescher's teacher and laboratory chief in Tübingen, the German biochemist Felix Hoppe-Seyler (1825–95), received the manuscript, but was sceptical about the rather revolutionary findings of a beginner. Therefore, he decided to repeat the experiments, and he printed Miescher's paper “Über die chemische Zusammensetzung der Eiter-zellen” only after he had verified them.

Hoppe-Seyler wrote in a footnote that the publication was delayed very much “through several unforeseen circumstances”. In a paper of his own he writes: “I have to emphasize that in all points as far as I have examined Miescher's statements I have to confirm the latter fully.”