The method of differential staining first described by Gram in 1884 has become an important means of classifying bacteria and, as in the case of the gonococcus, forms an important factor in their morphologic recognition.
The exact reaction or conditions governing the retention or loss of the violet dye, as a result of which bacteria are classed as gram positive or gram negative, is not entirely clear, nor is it definitely known whether the bacterial protein (protoplasm) or the bacterial cell wall is mainly concerned in the retention of the dye.
According to Wells,1 the gram positive reaction is due to the formation of an iodin-pararosanilic-protein compound not easily dissociated by water, and he suggests that the cell wall of gram positive organisms is impermeable to the action of decolorizing agents.
The fact that the disintegration of gram positive organisms renders them gram negative, as shown by Benians, and
KILDUFFE RA. A NEW ALKALINE SOLUTION OF IODIN FOR USE IN THE GRAM STAIN. JAMA. 1923;81(26):2182. doi:10.1001/jama.1923.02650260024008
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