Field's Stain A is used as staining solution for blood films for Spirochaetes, Protozoa and other purposes.Field Stains contain methylene blue and eosin. These basic and acidic dyes induce multiple colours when applied to cells. The fixative, methanol does not allow any futher change in slide. The basic component of white cells (cytoplasm) is stained by acidic dye and they are described as eosinophilic or acidophilic. The acidic component (nucleus with nuclei acid) takes blue to purple shades of the basic dye and are called basophilic. The neutral component of the cells are stained by both the dyes.This staining method is used for screening thick films of malarial parasites.