Answer:
He discovered the cell nucleus and realized that inside the nucleus there was an unknown chemical substance. That substance was DNA.
Step-by-step explanation:
Who discovered the DNA was Friedrich Miescher, a Swiss biochemist with great talent. Miescher, using substance precipitation techniques, such as pH changes in the medium, was able to discover and isolate the cell nucleus. Inside the nucleus he was able to isolate a previously unknown substance. It was the nucleic acid, DNA, which, at the moment, with the technology available until then, presented itself only as a white, flocculent precipitate, which Miescher would later call nuclein.