Within recent years evidence has come from several lines of research that the gene is either composed of, or is at least intimately associated with, desoxyribose nucleic acid (DNA). Experiments in microbial genetics have shown that only the DNA fraction of the bacterial protoplast is capable of transforming other bacteria to the genetic type from which the DNA was originally derived (2). Further, both chemical extraction and photometric studies have supported the view that within a plant or animal the amount of DNA per nucleus occurs in simple multiples of a basic (haploid) amount (see references 30, 34 for review). Such consistent quantitative behavior could account, at least in part, for the remarkable genetic constancy of successive cell generations and has been presented as evidence for close relationship between DNA and the stable characteristics of the gene (see reference 30 for review).The nucleus has been known for some time to embody several other forms of stability. Studies on uptake of radioactive phosphorus (p32) have shown a striking metabolic stability in the DNA molecule. Autoradiographic studies (see references 11, 33, 16, 8 for review) indicate that although incorporation of p32 into DNA is high in tissues where DNA synthesis is occurring, it is very low in some non-dividing tissues. Furthermore, chromatographic separation and quantitation of the purines and pyrimidines of DNA indicate that the proportions of the purine and pyrimidine bases seem to be constant for a species (6,35). In contrast to the stability of DNA, ribose nucleic acid (RNA) and some protein fractions appear to vary and Ris (22) has suggested that constancy of DNA represents nuclear stability presumably related to the stable aspects of the gene, while the variability of some protein and RNA fractions represents instabilit~ and change in the nucleus according to cell function.