CULTIVATION OF PNEUMOCOCCUS 



237 



transparent small discs which have been compared to drops of 

 dew (Fig. 65). 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 blo'od agar. It usually 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 otherwise 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. 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 statement also 

 applies to cultures in gelatin at 22 C., 

 growth in a stab culture appearing as a 

 row of minute points which remain of 

 small size ; there is, of course, no lique- 

 faction of the medium. In bouillon, 

 growth forms a slight turbidity, which 

 settles to the bottom of the vessel as a 

 slight dust-like deposit. On potatoes, as 

 a rule, no growth appears. Cultures may 

 be maintained for one or two months, ifj 

 fresh sub-cultures are made every four ; 

 or five days, but they tend ultimately to die out. They also 

 rapidly lose their virulence, so that four or five days after 

 isolation from an animal's body their pathogenic action is 

 already diminished. Eyre and Washbourn, however, succeeded 

 in maintaining cultures in a condition of constant virulence for 

 at least three months by growing the organisms o'n agar smeared 

 with rabbit blood. The agar must be prepared with Witte's 

 peptone, must not be heated over 100 C., and after neutralisa- 

 tion (rosolic acid being used as the indicator) must have '5 per 

 cent, of normal sodium hydrate added. The tubes when in- 

 oculated are to be kept at 37 '5 C. and sealed to prevent 

 evaporation. In ordinary artificial media pneumococci usually 

 appear as diplococci without a capsule but in preparations made 



TG. 65. 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. 



