CHAPTER XXV. 



THE DIPLOCOCCUS OF PNEUMONIA (PNEUMOCOCCUS, STREPTO- 

 COCCUS LANCEOLATUS, MICROCOCCUS LANCEOLATUS). THE 

 PNEUMOBACILLUS (FRIEDLANDER BACILLUS). 



The Diplococcus of Pneumonia. 



THE diplococcus of pneumonia was observed in 1880 almost simul- 

 taneously by Steinberg and Pasteur in the blood of rabbits inoculated 

 with human saliva. In the next few years Talamon, Friedlander, 

 A. Fraenkel, Weichselbaum, and others subjected this micro-organism 

 to an extended series of investigations and proved it to be the chief 

 ^tiological factor in the production of lobar or croupous pneumonia 

 in man. 



The outcome of the various investigations proved that the acute lung 

 inflammations, especially when not of the frank lobar pneumonia type, 

 are not excited by a single variety of micro-organism, and that the 

 bacteria involved in the production of pneumonias are also met with 

 In inflammations of other tissues. 



In any individual pneumonic inflammation it is also found that more 

 than one variety of bacteria may be active, either from the start or as a 

 later addition to the original primary infection. 



Among all the micro-organisms active in exciting pneumonia, the 

 diplococcus of pneumonia is by far the most common, being almost 

 always present in primary lobar pneumonia and as frequently as any 

 other germ in acute bronchopneumonia and metastatic forms. Besides 

 the different varieties of pneumococci the following bacteria are capable of 

 exciting pneumonia: streptococcus pyogenes, staphylococcus pyogenes, 

 bacillus pneumonias, bacillus influenzas, bacillus pestis, bacillus diph- 

 therias, bacillus typhi, bacillus coli, and the bacillus tuberculosis. Since 

 the varieties of bacteria exciting acute pneumonia, with the exception 

 of the pneumococcus, are met with more frequently in other inflam- 

 mations and have been described elsewhere, they will only be noticed 

 in this chapter so far as their relation to pneumonia demand. 



Morphology. Typically, the pneumococcus occurs as spherical or oval 

 <;occi, usually united in pairs, but sometimes in longer or shorter chains 

 -consisting of from three to six or more elements and resembling the strep- 

 tococcus. The cells, as they commonly occur in pairs, are somewhat oval 

 in shape, being usually pointed at one end hence the name lanceolatus 

 or lancet-shaped. When thus united the junction, as a rule, is between 

 the broad ends of the oval, with the pointed ends turned outward; but 

 variation in form and arrangement .of the cells is characteristic of this 



