CULTIVATION OF PNEUMOCOCCUS 



201 



difficulty can always be overcome by having the groundwork 

 of the preparation tinted. 



The Cultivation of Fraenkel's Pneumococcus. It is usually 

 difficult, and sometimes impossible, to isolate this coccus directly 

 from pneumonic sputum. On culture media it has not a vigorous 

 growth, and when mixed with other bacteria it is apt to be 

 overgrown by the latter. To get a pure culture it is best to 

 insert a small piece of the sputum beneath the skin of a rabbit 

 or a mouse. In about forty-eight hours the animal will die, 

 with numerous capsulated pneumococci 

 throughout its blood. From the heart- 

 blood cultures can be easily obtained. 

 Cultures can also be got post mortem from 

 the lungs of pneumonic patients by 

 streaking a number of agar or blood- 

 agar tubes with a scraping taken from 

 the area of acute congestion or commenc- 

 ing red hepatisation, and incubating them 

 at 37 C. The colonies of the pneumo- 

 coccus appear as almost transparent small 

 discs which have been compared to drops 

 of dew (Fig. 67). This method is also 

 sometimes successful in the case of 

 sputum. 



The appearances presented in cultures Fm . 67 ._ Stroke culture of 

 by different varieties 01 the pneumococcus 

 vary somewhat. It always grows best 

 on blood serum or on Pfeiffer's blood 

 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. 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 liquefaction of the medium. On 

 agar plates colonies are almost invisible to the naked eye, 

 but under a low power of the microscope appear to have a 

 compact finely granular centre and a pale transparent periphery. 

 In bouillon, growth forms a slight turbidity, which settles to the 



Fraenkel's pneumococcus 

 on blood agar. The 

 colonies are large and un- 

 usually distinct. Twenty- 

 four hours' growth at 

 37 C. Natural size. 



