Its discovery was one of the most important landmarks in understanding tuberculosis and in molecular biology.
From the crushed bacilli, specifically the protein tuberculin, he isolated two toxic substances, namely a basic compound which he called tuberculosamine, and a nucleotide he named tuberculisäure, later to be anglicised to tuberculinic acid.
Ruppel also found that his new compound was the most toxic component of the bacillus, 2.5 to 6 times more potent than tuberculin, the proteinaceous toxin.
[2] In 1925, Treat Baldwin Johnson and Coghill were detected a minor amount of a methylated cytosine derivative as a product of hydrolysis of tuberculinic acid, from avian tubercle bacilli, with sulfuric acid.
[3][4] This report was seriously challenged because others failed to reproduce the result after a series of tests.