Word Study
gram's method
OXFORD DICTIONARY
gram's method, n. Biol. a method of differentiating bacteria by staining with a dye, then attempting to remove the dye with a solvent, for purposes of identification.
Idiom
Gram-positive (or negative) (of bacteria) that do (or do not) retain the dye.
Etymology
H. C. J. Gram, Da. physician d. 1938
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