Methods have been described by which capsules and mucoid envelopes of bacteria can be fixed and stained positively and differentially, proving they are of different natures. The capsule is of definite shape and outline, the slime is amorphous. Some bacteria may have capsules, some may produce slime, and in others the capsulated organisms may be embedded in amorphous slime, as, for example, in the Fried-lander bacillus and in the Pneumococcus, type III. These properties are probably more or less characteristic for certain organisms or groups of organisms. Of course, loss of capsules, and loss of slime production do occur.

All bacteria which have capsules seem to possess special antigens (cp. Kauffmann's A-antigen). This was particularly shown for members of the coli-oerosrenes-Friedlander groups and Streptococcus para-faecalis (Skadhauge). Organisms with L-antigens possess generally no capsular or mucoid envelopes of the type described, with one exception, viz. strain Bi 316/42.

By means of the capsule- and slime-staining methods here described, a densely staining edge was demonstrated in the bacteria examined, which—it is suggested—may comprise the cell wall and its adjoining cytoplasmic layer. Organisms supposed to have no cell walls (Myxococci) do not show this appearance.

The so-called ‘swelling reaction’ is a reaction between antiserum and homologous bacteria, by which the capsule becomes easily demonstrable. It seems doubtful that actual swelling takes place.