On Thymus Nucleic Acid

A consideration of the earlier investigations of the nucleic acids would lead us to the conclusion that these substances yield among their hydrolytic products four purin derivatives, namely, xanthin, hypoxanthin, guanin, and adenin. Of these four bases hypoxanthin was the first discovered in this connection and was for a long time looked upon as the most constant in its occurrence, and, therefore, the most important; so that chemists frequently omitted identification of the bases and spoke of them collectively as hypoxanthin. Kossel was so strongly convinced of the presence of all four of these bases, among the decomposition products of nucleic acids that he employed the expression “nuclein bases”’ to include them all, and formulated an hypothesis to the effect that there are in reality four nucleic acids, each of which produces one nuclein base, and that the material ordinarily considered nucleic acid was in most cases a mixture of four nucleic acids so that four bases were necessarily obtained as hydrolytic products. All of the earlier work, however, was carried on with quantities of materials so small as to render exactness impossible; therefore, as methods were discovered by which nucleic acids could be prepared in any desired amount and as schemes became perfected for the separation of the decomposition products, the existing literature on the subject seemed to require some revision. Thus, Kossel had regarded thymus nucleic acid as one of the four nucleic acids required by his hypothesis and called the substance adenylic acid to indicate that of the four nuclein bases, it yields only adenin. But with better facilities, Kossel and Neumann’ showed later that adenylic acid yields both guanin and adenin.