CULTIVATION OF PNEUMOCOCCUS 



229 



37° C. This method is also sometimes successful in the case of 

 sputum. 



The appearances presented in cultures by different varieties of 

 the pneumococcus vary somewhat. It always grows best on 

 blood serum or on Pfeiffer's blood agar. It often grows well 

 on ordinary agar or in bouillon, but not so well on glycerin 

 agar. In a stroke culture on blood serum growth appears as an 

 almost transparent pellicle along the track, with isolated colonies 

 at the margin. On agar media it is more manifest, but other- 

 wise has similar characters. On agar plates colonies are very 

 transparent, but under a low power of 

 the microscope appear to have a com- 

 pact finely granular centre and a pale 

 transparent periphery ; after forty-eight 

 hours they increase slightly in size and 

 present a depressed centre (Fig. 59). 

 The appearances are similar to those of 

 a culture of streptococcus pyogenes, but 

 the growth is less vigorous, and is more 

 delicate in appearance. A similar state- 

 ment also applies to cultures in gelatin 

 at 22° O, growth in a stab culture ap- 

 pearing as a row of minute points which 

 remain of small size ; there is no lique- 

 faction of the medium. In bouillon 

 (which must be made from fresh meat — 

 rabbit muscle being suitable) growth 

 forms a slight turbidity, which settles to 

 the bottom of the vessel as a dust-like 

 deposit. On potato, as a rule, no growth 

 appears. Cultures may be maintained 

 for long periods, if fresh sub-cultures are 

 made every four or five days, but they tend ultimately to die out. 

 They sometimes rapidly lose their virulence, so that four or five 

 days after isolation from an animal's body their pathogenic action 

 disappears, but this is not always the case, especially if serum 

 bouillon be used for maintaining sub-cultures ; virulence may 

 also be maintained by the whole blood of an infected rabbit 

 even when this is almost dried up, or in the spleen of an in- 

 fected mouse kept dry in vacuo. In ordinary artificial media 

 pneumococci usually appear as diplococci without a capsule, but 

 in preparations made from the surface of agar or from bouillon, 

 shorter or longer chains may be observed (Fig. 60). After a 

 few days' growth they lose their regular shape and size, and 



Pig. 59. — Stroke culture of 

 Fraenkel's pneumococcus 

 on blood agar. The 

 colonies are large and un- 

 usually distinct. Twenty- 

 four hours' growth at 

 37° C. Natural size. 



