From the time of Loeffler's discovery of the diphtheria bacillus in 1884, its staining has been a matter of great interest. Many special staining methods have been devised all of which have aimed at making the diagnosis of diphtheria easier and more definite.
For some time, Loeffler's methylene blue was the only stain used for the clinical differentiation of the diphtheria organism. In 1893, Neisser developed a stain the purpose of which was to bring out the polar granules more definitely. He believed that his stain would differentiate the true diphtheria bacillus from pseudoforms. It was subsequently shown that these polar granule forms of the diphtheria bacillus were not always found in cases of diphtheria and that they were sometimes found in cultures of Hoffman's bacillus. However, in Hoffman's bacillus the granules are smaller, not so numerous and appear later during the incubator growth than do those of the diphtheria
GREENTHAL RM. A NEW STAIN FOR THE DIPHTHERIA BACILLUS AND A CONSIDERATION OF THE PRINCIPLES INVOLVED IN THE STAINING OF THIS ORGANISM. Am J Dis Child. 1919;18(1):25–29. doi:10.1001/archpedi.1919.04110310028005
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