Acute lobar pneumonia : prevention and serum treatment / by Oswald T. Avery [and others].

Date:
1917
Catalogue details

Licence: Public Domain Mark

Credit: Acute lobar pneumonia : prevention and serum treatment / by Oswald T. Avery [and others]. Source: Wellcome Collection.

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    elongated bacillary forms may occur. In young, actively growing broth cultures of pneumococcus, chain formation is common, while in the same culture, after 18 hours’ incubation, the organisms are usu- ally arranged in pairs with only an occasional short chain. In older cultures of pneumococcus, the organisms often appear Gram-negative, swollen, with degenerated and involuted forms, resulting from disin- tegration and death of the cells. Pneumococcus is readily stained by all the usual aniline dyes. It possesses no flagella, is non-motile, and does not form spores. Capsules are easily demonstrable in animal exudates and, by appropriate methods, may be found in cultures from media enriched with blood or serum. ‘The capsular substance is most marked in recently isolated virulent strains, and is readily lost on prolonged cultivation. In Pneumococcus mucosus, Type ITI, the capsule is so pronounced as to be frequently demon- strable by Gram’s stain, by which method it appears as a negatively staining halo about the Gram-positive cell body. The exact signifi- cance of the capsule of pneumococcus is not known. That it may serve as a protective mechanism of the organism and that it may in some way be related to virulence, is suggested by the fact that cap- sular development is always much more marked when the organism is grown in animal tissues in which presumptively there is some opposition to its development. Study of a large number of strains of pneumococci shows that there are average differences in capsular development between Types I, II, III, and IV (page 17). Although in some strains of Type IV pneumococci capsular formation is well marked, in others it is quite irregular and at times impossible to demonstrate, even under the most favorable conditions. Type I pneumococci usually show well formed capsules, and in Type IT pneu- mococci the capsules are quite easily demonstrable and are generally somewhat larger and denser than in Type I. In Type III pneumo- cocci capsules are always well developed, are very large in compari- son with the size of the organisms, and may appear as voluminous envelopes about the cell bodies. In our experience the amount of capsular development seems to parallel the virulence of these organ- isms for man, as measured by the mortality occasioned by the dif- ferent types in human infection. In addition, it seems to be true that the greater the amount of capsular development, the less the amount of passive protection afforded by immune serum.