Abstract
A technic has been described by which capsules can be readily demonstrated not only on “capsulated” organisms but also on certain bacteria and under certain conditions where they are supposed not to exist. 1 More extensive studies have confirmed the earlier findings, one of the most significant of which was the observation that R types of pneumococcus are as definitely capsulated as S types. Although this method remains the most reliable general capsular stain, with either of the following methods, equally or more beautiful pictures have been obtained, notably with B. anthracis from the animal body: modifications of Wright's stain; MacNeal's Tetra-chrome Stain; Giemsa Stain; Casares-Gil Flagella Stain. These methods prove that bacterial capsules differ. No one method should be expected to stain all equally satisfactorily. If smears are made from a suspension in 0.25% nutrose, better pictures of the capsule are sometimes obtained.
2. Structure of Capsule. The distance between soma and capsular membrane is, like the size of the soma itself, variable. The capsule of virulent pneumococcus enlarges when the organism is injected into the peritoneum of the mouse. The capsule may also shrink and the capsular membrane may then lie practically upon the bacterial body. We have frequently seen 2 distinctly stained capsular membranes, one lying close to the soma and the other at some distance from it, with a large space between. The observations in general suggest that the capsule may in reality be a potential cavity whose size depends on the amount of capsular secretion or other fluid it contains.
3. Relation of capsule to cortex. Observations were reported 2 suggesting that many gram positive organisms contain a gram negative medulla and are gram positive only at the surface or cortex.
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