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Eosinophils are also known as eosinophilic granulocytes, or eos. Eosinophils are easy to recognize in the peripheral blood because of their large, bright reddish-orange granules.
The diameter of the eosinophil is 9-15 microns, and the nuclear to cytoplasmic (N:C) ratio is 1:3. Eosinophils are generally the largest granulocytes found in normal blood.

Their cytoplasm is usually colorless or light blue. However, the color is usually masked by the large granules that are present. These granules take up the acid components of Wright stain, and are therefore reddish-orange.