Iv. Penetration of Brilliant Cresyl Blue into Nitella Flexilis by Marian Irwin

A basic dye is usually obtained in the form of the salt some of which may be transformed in aqueous solution to free base (the m o u n t depending on the "apparent" dissociation constant of the dye and the pH value), and in the range of pH values generally employed with living cells (approximately between pH 5 and 9.5) both forms of dye must be considered. In this range methylene blue, for example, exists only as a salt. I t isverystrongly basic 1 so that even at pH 9.5 no free base is formed. Lauth's violet, on the other hand, isless basic, with a basic dissociation constant ~ of 1.9 × 10 -s. Since the nature of the transformation of the dye salt into the free base is still in dispute * the structure of the salt and free base of the dye will not be discussed. Furthermore, the dissociation constant of cresyl blue has not been determined by such methods as the oxidation-reduction potential or the glass electrode, so that the basicity of the dye is not accurately known. I t is, however, possible to determine approximately the relative ratio of the dye in form of free base/salt by shaking the chloroform with the dye solution and de-