Quantitative adsorption of methylene blue by dead yeast cells.

Quantitative studies of dye adsorption by bacteria have been made (Kennedy and Barbaro, 1953; Barbaro and Kennedy, 1954; Kennedy and Woodhour, 1956; Barbaro et al., 1956) in order to measure the degree of gram-positiveness, and to study the influence of several factors on the quantity of dye retained by the microorganisms. No attention has been given, however, to the applicability of the physicochemical adsorption law in the cases studied. This report is divided into three parts. The first part shows that the adsorption of methylene blue by dead yeast cells follows the well known Freundlich law. The second part shows that it is possible to make very precise determinations of total yeast concentration by the measurement of the adsorption of methylene blue. The third part shows the possibility of determining the percentage of dead cells by a new colorimetric method. Freundlich's law. The classic form of the physicochemical adsorption law (Freundlich's law) is (Glasstone, 1943):