STUDIES ON OXIDATION-REDUCTION IN MILK II. THE CHOICE OF AN INDICATOR FOR THE REDUCTION TEST. THE REDUCTION OF JANUS GREEN B IN MILK

Abstract

In 1900 Neisser and Wechsberg suggested that the reduction of methylene blue might be used as an indication of the bacterial content of milk. The intervening twenty-nine years have witnessed the adoption of their suggestion and the growing use of their method till today it is one of the standard tests in the bac-teriological analysis of milk. It is significant that methylene blue has remained undeposed as the indicator par excellence for this purpose. This dye has retained its place, not because of precise knowledge of its behavior in milk, but rather because its superiority has been amply demonstrated by experience and by trial and error methods of comparison. In the light of the newer knowledge of dye reduction the time seems ripe to reconsider the question of indicators for milk quality. A splendid review of the history of dye reduction by bacteria is to be found in the paper by Fred (1912). A very extensive bibliography on methylene blue as an indicator of reduction has been given by Clark, Cohen and Gibbs (1925). This paper also discusses the place of methylene blue as an indicator in biological oxidations and reductions. A reiteration here of material so readily available would be out of place. The reader is, therefore, referred to the cited sources for such information.