Chapter V — 39 — Physical Chemistry 



only of potassium nitrates (1% at pH 9), the rose derivative of 

 Janus green will stain the cytoplasm of yeasts and in the absence of 

 air will completely lose its color. It is, therefore, reduced to its leu- 

 coderivative. If the medium is aerated, the leucoderivative is oxi- 

 dized and returns to its rose form. This reduction from the rose to 

 the leucoderivative takes place at rH 5.2. This limit seems to be 

 reached at the end of a long time and under experimental condi- 

 tions. It seems, therefore, to be the lowest obtainable rH value. 

 The method is a safe one to follow as yeasts treated in this man- 

 ner can bud in a very active way after having excreted the dye. 



