TIIK DIPLOCOCCUS OF PXEUMOMA 357 



combination with the streptococcus, the influenza bacillus, or other 

 bacteria. 



In certain epidemics pneumococcic bronchitis and pneumonia simu- 

 late influenza very closely and cannot be dilYerentiated except by bac- 

 teriological examinations. 



Primary pneumococcic pleurisy is frequent in children ; it is very often 

 purulent, but may be serous or serofibrinous. Its prognosis is better 

 than that in cases due to other organisms. Frequently we have strep- 

 tococci and staphylococci associated with the pneumococci. 



Varieties of the Pneumococcus. As among all other micro-organisms 

 minutely studied, different strains of pneumococci show quite a wide 

 range of variation in morphology and virulence. Some of the variations 

 are so marked and so constant that they make it necessary to recognize 

 several distinct varieties of the pneumococcus, and to class as pneumo- 

 cocci certain varieties which have before this been classed as strepto- 

 cocci e. g., the so-called streptococcus mucosus capsulatus (streptococcus 

 mucosus Schottmiiller), when first isolated from pneumonic exudate or 

 elsewhere, and planted on artificial culture media containing serum, 

 grows as a rounded coccus with a small dense distinct capsule, princi- 

 pally in short or medium chains; it produces a large amount of 

 mucus-like zooglia, forming very large spreading colonies; it promptly 

 coagulates fluid serum media containing inulin. It is also very virulent 

 for mice, but only moderately virulent for rabbits. After a number of 

 culture generations on ordinary nutrient agar it apparently loses most 

 of these characteristics. It then grows in small colonies principally as 

 naked diplococci whi?h may be elongated and pointed, produces no 

 zooglia, and loses most of its virulence for mice and rabbits. It still 

 coagulates inulin serum media, and when transferred to serum media 

 regains its former morphological characteristics. For these reasons we 

 consider this organism a distinct variety of the pneumococcus. This 

 variety of pneumococcus has been isolated by us from the lungs after 

 death following lobar pneumonia, out of twenty consecutive autopsies, 

 as the only organism present twice, and with another variety of pneu- 

 mococcus once. Together with other varieties it was isolated from 

 four out of twenty specimens of pneumonic sputum, and from sixty 

 specimens of normal throat secretion five times. 



Another group of pneumococci quite constantly produces large forms 

 and large capsules. Still another group produces principally small 

 forms and small capsules. Another group might be made of morpho- 

 logically typical pneumococci which do not coagulate inulin serum 

 media. 



Immunity. Early in the history of this organism experiments were 

 begun for the production of immunity in animals by means of preventive 

 inoculations. Later it was found that after successive injections of 

 gradually increasing doses of virulent pneumococci into certain animals 

 (horse, sheep, goat, rabbit), a serum of some protective and curative 

 power in experimental animals was obtained. The mode of action of 

 this serum is still the subject of study. According to Wright, Neufeld, 



