SIX FIGURES
I n recent years considerable attention has been focused upon nucleic acid metabolism and the protein-forming system in general in a variety of tissues undergoing active growth or secretion. This work has received especial stimulation from the development of more refined techniques, both chemical and physical, for the detection and quantitative estimation of these substances. It seemed that the uterus, which is cyclically subjected to hormonal stimuli, might offer suitable material for such a study as well as possibly yielding information on the complex, but basic, problem of the mechanism whereby a hormone produces its effect upon a cell.
Chiefly through the work of Caspersson and his associates (see Caspersson, '50, for full bibliography) , a working hypothesis of the mechanism of action of the protein-forming system has been advanced, which involves the active participation of the heterochromatin and nucleolar apparatus. Briefly, this theory assumes the regulation of desoxyribonucleic acid (DNA) and ribonucleic acid (RNA) synthesis by the heterochromatin of the nucleus. During periods when protein for-'The author is deeply grateful t o Professor T. Caspersson of this institute for his having made the facilities of his laboratory available for this work and for his suggestions throughout its course.