36 BIOLOGY OF PNEUMOCOCCUS 



DIRECT CULTURES 



Instead of the practice of animal inoculation, washed sputum, 

 blood, or broth suspensions of infected material may be streaked 

 on plates poured with fresh blood agar or serum-dextrose agar. 

 For the cultivation of organisms directly from the circulating 

 blood, the blood withdrawn by venous puncture may be added to a 

 fairly large volume of dextrose broth in flasks, or mixed with mol- 

 ten dextrose agar and poured into Petri dishes. Pneumococcus, be- 

 ing facultative in its oxygen needs, grows on the surface as well as 

 in the depths of the medium. 



From agar plates single colonies of pneumococci may be picked 

 and replanted on agar, seeded on serum or blood-agar slants or in 

 serum or glucose broth. These media serve for the further propa- 

 gation of the original broth cultures when pure. Small inoculums 

 grow more successfully on solid than on liquid media. Incubation 

 should be carried on at a temperature of about 37.5° ; 25° and 41° 

 represent the lower and upper limits favorable to growth. A rarity 

 were the strains isolated from blood and exudates by Eaton* in 

 Zinsser's laboratory, which grew only at 25°. At 37.5° the organ- 

 isms failed to grow unless incubated in an atmosphere containing 

 about 10 per cent of carbon dioxide. A somewhat similar strain 

 was that previously reported by Kindborg. 712 Isolated from rusty 

 sputum by mouse inoculation, the organism displayed all the char- 

 acters of a typical pneumococcus, yet it grew readily at 22° and 

 rapidly and energetically liquefied gelatin. While pathogenic for 

 mice, it was avirulent for rabbits. 



Cultivation 



Pneumococcus, being a strict parasite, is somewhat fastidious in 

 nutritional requirements, as well as sensitive to the physical and 

 chemical conditions of its surroundings. The essential ingredients 

 of culture media are meat extractives prepared from fresh muscle 



* Quoted by Zinsser and Bayne-Jones.i579 



