Methylene Blue Loeffler reagent is used for staining acidoresistant bacteria according to Ziehl-Neelsen, utilizing the dye's property to stain almost all the bacterial cell's elements in a mildly alkaline medium (Methylene Blue Loeffler reagent has pH value of 8-8.5).

The Löffler's alkaline methylene blue staining method is a simple staining technique that can be used to differentiate bacterial, viral, and fungal infections. ... Specimens collected from patients by swabbing are smeared onto microscope slides and the methylene blue solution is dropped on the slide.

It is a cationic dye that stains cells blue because the positively charged dye is attracted to negatively charged particles such as polyphosphates, DNAs, and RNAs. 

METHYLENE BLUE is used to treat methemoglobinemia. This is a condition in which the blood loses its ability to carry oxygen through the body.

METHYLENE BLUE ALKALINE LOFFLERS STAINING SOLUTION