BIOLOGY OF PNEUMOCOCCUS 31 



varying size (0.5 to 1.25|j), or they may be so elongated as to re- 

 semble bacilli. One authority describes the cells as "small," another 

 as "rather large," but the actual size varies with the circumstances 

 under which the organism is observed. In any given preparation, 

 along with typical forms, other members displaying every degree 

 of involution or degeneration may be present, while in aged cul- 

 tures aberrant forms may be the rule. 



Pneumococcus has no spores, no vacuoles, no visible granules, no 

 flagella, and is non-motile. It reproduces by the primitive method 

 of transverse fission. 



The most distinctive morphological feature of the organism is 

 the capsule. The capsule is more prominent when the cocci are ex- 

 amined in the body fluids of infected animals, or in media enriched 

 with body fluids, becoming faint or disappearing when the strain is 

 grown on less rich substrates. The capsule envelops the single, 

 paired, or chained cocci, frequently with a uniform periphery, al- 

 though sometimes it shows indentations between the twin cells or 

 between the paired individuals in chains. 



STAINING METHODS 



Pneumococcus is readily stained with the usual aniline dyes and 

 is Gram-positive. Exposure to the action of specific immune serum, 

 or even to acidulated pepsin or alkalinized trypsin mixtures fails 

 to rob the cocci of this property (Wilke 1520 ). Only when they are 

 subjected to the digestive action of leucocytes, or after death and 

 partial disintegration in old cultures, do they give up the dye to 

 decolorizing agents. For peritoneal fluids, sputum, and cultures 

 the Gram stain is generally used. The authors prefer Burke's 

 modification 191 to that of Sterling* or to the original formula. 545 



Dold 324 " 5 recently devised a staining method by which he claimed 

 to be able to divide Gram-positive cocci into four groups and to 

 demonstrate tinctorial differences between pneumococci and strep- 

 tococci. He treated preparations made from cultures on solid me- 



* Original reference unknown. 



