THE PNEUMOCOCCUS 55 



cal importance. The Staphylococcus pyogenes aureus grows readily at room tempera- 

 ture, but better at 37 C. It coagulates milk and renders bouillon uniformly turbid. 

 It grows on all media, as blood-serum, agar, potato, etc. It has been proposed to 

 distinguish it from skin staphylococci by its power of producing acid in mannite. 

 Ordinarily the individual cocci are about i// in diameter, but they vary greatly in 

 size according to the age of the culture and other conditions. The aureus, as it 

 is frequently called, is not only often found in circumscribed processes, but it is a 

 frequent cause of septicaemia, osteomyelitis, endocarditis, etc. 



In infection of bone tissue the Staphylococcus is by far the most frequent cause. 

 It is well to remember that insignificant staphylococcal infection may lead to sep- 

 ticaemia. In the tropics, where resistance is often lowered and staphylococcal skin 

 infections common, continued fevers are often septicaemias. It is the organism 

 most frequently concerned in terminal infections. The lowered resistance of the 

 patient permits of their passage through barriers ordinarily resistant. Not only 

 should this be kept in mind when such organisms are isolated at an autopsy, but 

 as well the fact that their entrance may have been agonal or subsequent to death. 



The Pneumococcus of Fraenkel. (Weichselbaum differentiated 

 organisms causing pneumonia in 1886.) This is by far the most com- 

 mon cause of pneumonia, whether it be of the croupous, catarrhal, or 

 septic type. It is also frequently found in meningitis, empyema, endo- 

 carditis and otitis media. It should not be confused with the pneumo- 

 bacillus of Friedlander, which, although possessing a capsule like the 

 pneumococcus, differs from it by being Gram negative, being a bacillus 

 and having large viscid colonies. The pneumococcus is the cause of 

 more than 80% of the cases of pneumonia. It does not grow below 

 20 C. and is best cultivated on blood-serum, or blood-streaked agar. 

 On plain agar it grows as a very small dew-drop-like colony, which is 

 slightly grayish by reflected light. It produces considerable acid, thus 

 acidifying and usually coagulating litmus milk. It produces acid in 

 inulin media which the streptococcus fails to do. The colony is smaller 

 and more transparent than a streptococcus colony. In sputum or 

 other pathological material it is best recognized by the presence of a 

 capsule inclosed in which are two lance-shaped cocci with their bases 

 apposed. In artificial culture we rarely get the capsule. It also some- 

 times grows in short chains like a streptococcus. The* best medium 

 for differentiating is the serum of a young rabbit; in this it grows as a 

 diplococcus, while streptococci show chains. The best method of 

 isolating it in pure culture is to inject the sputum into the marginal 

 ear vein of a rabbit or subcutaneously into a mouse. Death results 

 from septicaemia in about two days and the blood teems with pneu- 

 mococci. Usually the pneumococcus quickly loses its virulence, and 



