CUL 77 VA TION OF PNE UMOCOCCUS. 209 



In sputum preparations the capsule of both pneumo- 

 cocci may not be recognisable, and the same is sometimes 

 true of lung preparations. This is probably due to changes 

 which occur in the capsule as the result of changes in the 

 vitality of the organisms. Sometimes the difficulty of 

 recognising the capsule when it is present, is due to the 

 refractive index of the fluid in which the specimen is 

 mounted being almost identical with that of the capsule. 

 This difficulty can always be overcome by having the 

 ground-work 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 com- 

 mencing red hepatization, and incubating them at 37 C. 

 The colonies of the pneumococcus appear as almost trans- 

 parent small discs which have been compared to drops of 

 dew (Fig. 57). 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 

 usually grows well on ordinary agar or in bouillon, but not so 

 well on glycerine 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 



