EEMAEKS ON TECHNIQUE 13 



We use the term capsule when a clear space is seen around every 

 one, or around the majority, of the organisms in question. Several 

 conditions may produce the same appearance : retraction of the 

 surrounding medium, or of the coagulated substance of the secretion. 

 Bacteria appear to be encapsuled when they lie in spaces produced by 

 drying or heating. We should always note whether, in those parts 

 of the preparation which are free from bacteria, similar clear spaces 

 occur ; naturally here and there Bacteria may have fallen out, but 

 generally there will be no hesitation about the nature of these 

 retraction spaces. 



The capsules (mucous envelopes) are formed by the swelling of the 

 ectoplasm, the outer layer of the bacterium. The majority of 

 organisms which are generally considered to be capsule-free have a 

 slight ectoplasm, which under special circumstances may become 

 more obvious and quite visible. This is so with Staphylococcus, 

 Streptococcus, Coli communis, and others. This fine differentiation is, 

 however, not very apparent in the ordinary preparation, where we 

 only see the envelope when it is well developed. The bacteria with 

 a swollen ectoplasm appear to have a clear space around, which 

 space, according to the amount of mucus it contains and the method 

 of staining, will appear quite clear or coloured to a varying degree. 

 We only use the expression ' well-marked capsule ' when such an 

 appearance is found. 



The development of an ectoplasm is much less marked in Pneumo- 

 cocci from a conjunctival secretion than from a pneumonic sputum. 

 Preparations stained with a simple aniline dye show the capsules 

 most clearly when examined in water. Gram- stained preparations in 

 balsam show them less clearly or not at all (see Plate II.). In 

 Pneumococci from an ulcus serpens or mucocele, capsules are better 

 seen. The clear spaces around stain very badly (in the allied Strepto- 

 coccus mucosus the capsule stains readily). On account of this slight 

 tendency to the formation of capsules Heim placed the conjunctival 

 Frankel-Weichselbaum Diplococcus intermediate between the Pneumo- 

 coccus and the Streptococcus. The capsules, however, in pneumonic 

 sputum are less well marked in the acute stage than in that of 

 resolution, and the conjunctival Pneumococci agree completely with the 

 same organism from other sources. 



Capsules are always very clearly seen in Friedlander's Pneumo- 

 lacillus, but vary somewhat in appearance. In this group they are 

 quite easily stained, not only with the special capsule stains, but also 

 with simple aniline dyes. The Pneumobacilli in Plate I. and in Fig. 3 



