Abstract
A simple method is described by which a capsule-like structure is readily demonstrated about many bacteria. It is selectively stained pink, in contrast to the blue bacterial bodies. Use is made only of stain and fixative. No artificial steps, like preliminary treatment with serum, etc., designed to render the capsule more readily demonstrable, are taken.
The technic follows: Smear dried in air, covered with 10 drops of Wright's stain, which is left on until it has nearly but not quite evaporated to dryness when a pinkish color replaces the original blue of the stain. This usually takes about 3 or 4 minutes. Wash off as rapidly as possible with Clark and Lub's buffer pH 6.4 to 6.5. (Sometimes a better specimen is obtained if smear is also washed rapidly with distilled water.) Dry with fan without blotting. If washing with buffer is done before stain has evaporated, the capsule-like structures will not be stained. Excellent results may also be obtained by leaving the air dried smear in Wright's stain over night, removing and allowing to evaporate until a pinkish color is reached, then dipping rapidly through buffer and drying with fan.
If technic be carried out correctly the capsule-like structure stains as a pink area surrounding the blue bacteria and itself limited by a definite membranous pink-stained periphery, on the outer surface of which precipitated stain is sometimes observed. Outside this structure a clear zone is occasionally (as in Diplococcus pneumoniae) seen. If staining be too deep the whole organism (capsulelike structure and bacterial body) is stained purplish and no distinction can then be made out between the parts. If staining is not deep enough or washing too prolonged all stain is removed from the capsule-like structure, only the blue bacterial bodies being then visible.
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