TEXT-BOOK OF BACTERIOLOGY. 303 



micro- organism observed by them in many cases of pneumonia. 

 Preparations, 'especially of alveolar fluid, and sections from the 

 changed lung-- tissue had first shown them this kind of bacterium ; it 

 was afterward again found in the rusty expectoration of the 

 patients. It was, moreover, readily cultivated artificially outside 

 of the body. Successful experiments having been made on animals 

 with these cultures, the discoverers did not hesitate to see in this 

 micro-organism the originator of pneumonia and named it accord- 

 ingly. 



They called it " pneumococcus." But it is really a short bacillus 

 w r hose rod shape is sometimes very distinct. Especially in the 

 hanging bouillon drops (where growth can take place unhindered 

 and unrestrained on all sides) and in the tissue, too, long bacilli are 

 formed; even the smallest and youngest members show, under 

 high magnifying power, that one of their diameters visibly ex- 

 ceeds the other. The cells are found usually singly or in pairs, ex- 

 tensive threads being sometimes formed. 



This is the usual appearance of Friedlander's pneumonia bac- 

 teria, and it would be difficult to distinguish them microscopically 

 in a stained preparation from the cells of the Micrococcus prodig- 

 iosus. The pneumococci possess, however, still another peculiarity 

 of formation, perceived, it is true, only under certain conditions. 

 In the animal body, their membrane acquires large dimensions; it 

 swells up to an extensive capsule and surrounds the rod as a bright, 

 transparent halo. But one member, as a rule, is found in each capsule, 

 but sometimes several cells just after division are enveloped by a 

 common cover which is then of considerable size. This thickening 

 of the cell membrane, at first scarcely perceptible, was formerly 

 considered to be a peculiarity of pneumonia bacteria alone, and they 

 were therefore named " capsule cocci," but incorrectly so, there being 

 several kinds of bacteria having capsules, like these pneumococci, 

 and resembling them, besides, in the general absence of the gelatin- 

 ous sheath when growing outside of the animal body; for instance, 

 in cultures. 



The capsule is by no means a special peculiarity of Friedlander's 

 bacteria, and hence, per se, cannot serve to differentiate them, the 

 less so because it is not uniformly present and cases occur in which 

 it cannot be proved to exist, even by very close examination. 



The pneumococci have no voluntary motion; the formation of 

 spores has not been observed; the3 r belongto the semi- anaerobic spe- 

 cies and flourish in the absence of oxygen as well as under free access 

 of air. They readily absorb the common anilin colors, but double 

 stainings have thus far failed, as they decolor during Gram's method. 



