In 1869 Miescher discovered a substance which he termed nuclein (nucleoprotein), later shown to be the hereditary genetic material. He demonstrated it in pus cells. The discovery he first published in 1871. He was also first to suggest the existence of the genetic code (see Nature (Lond.), 1967, 215, 556).

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Miescher first isolated DNA and identified it as an acid through chemical analysis of salmon spermatozoa.  See Ralf Dahm, "Discovering DNA: Friedrich Miescher and the early years of nucleic acid research," Human Genetics, 122 (2008) 565-581.

In a letter to his uncle, the embryologist, Wilhelm His, written on December 17, 1892, and first published in this collected edition, Miescher described a kind of genetic code. He remarked how "some of the large molecules encountered in biology, composed of a repetition of a few similar but not identical small chemical pieces, could express all the right variety of the hereditary message, 'just as the words and concepts of all languages can find expression in twenty-four to thirty letters of the alphabet" (Judson, The eighth day of creation. Makers of the revolution in biology, p. 28). Miescher's letter to Wilhelm His was first published in vol. 1, pp. 116-17 of this work.

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