FEULGEN NUCLEAL REACTION I. QUANTITATIVE EXTRACTION OF FUCHSIN FROM FEULGEN-STAINED NUCL*OPROTEII~ BY TOSISUKE HIRAOKA, D.Sc

Recent advances in cytochemistry have revealed that two types of nucleic acids play important roles in the cell (for references, 1 and 2). Whereas these two types of nucleic acids, deoxypentose nucleic acid (DNA) and pentose nucleic acid (PNA), have similar ultraviolet absorption properties, they are distinguished from each other by certain color reactions based on their constituent sugars. Among these color reactions, the Feulgen nucleal reaction has come to be known as the most specific one for deoxypentose nucleic acid (for references, 3). Owing to its high specificity, the Feulgen reaction has been used not only for the determination of DNA in tissue extracts (reaction in vitro, 4 and S), but also for DNA determination in a single cell nucleus with the aid of microspectrophotometry (reaction in situ, for references, 6). While much effort has been made with noteworthy success on applications of this reaction to DNA determination in biological materials, less effort has been directed towards an experimental analysis of this reaction, thus leaving much to be learned about the mechanism of the reaction. In order to obtain some insight into this mechanism and at the same time to obtain further improvement in the reaction as a nuclear stain in the field of cytochemistry, it seems essential to determine the amount of fuchsin contained in a Fuelgen-stained sample as the result of the reaction, in terms of a fundamental unit of mass 1. With this in mind, the author has devised a new method for the quantitative extraction of fuchsin from Feulgen-stained samples (fuchsin extraction method, FEM). This paper deals with the description of this method. It also deals with some problems involving the Feulgen reaction, about which more may be learned by means of experimentation with the aid of the FEM.