408 A MANUAL OF BACTERIOLOGY 



Cultural characters.- The S. pneumonice is aerobic and 

 almost facultatively anaerobic. On glycerin agar at 37 C. 

 it forms minute, transparent, almost invisible colonies like 

 droplets of fluid ; on serum the growth has much the same 

 characters, but is somewhat more abundant. It hardly 

 grows on gelatin at the ordinary temperature, but in a 

 20 per cent, gelatin at 25 C. minute white colonies develop 

 without liquefaction. In broth it produces a' slight cloudi- 

 ness ; it does not grow on potato but develops in milk, 

 which is usually coagulated ; neutral litmus glucose- agar 

 becomes red during growth, indicating the production of 

 acid. The fermentation reactions are given in the Table 

 on p. 235. Hiss's medium (p. 291) with inulin is fermented 

 and coagulated ; most other streptococci fail to ferment 

 inulin. On the ordinary culture media it retains its 

 vitality for a short time only, not more than about a week ; 

 but if a little blood be smeared over the surface of the 

 agar the vitality may be prolonged for a month or even 

 longer. Washbourn recommended an agar rendered alka- 

 line to the extent of 4 c.c. of normal caustic soda per litre, 

 after neutralisation, rosolic acid being the indicator. This 

 medium is smeared with blood, placed in the incubator 

 for twenty-four hours to ascertain whether it be sterile, 

 then inoculated, capped, and kept at 37 C. Foa's method 

 for keeping Frankel's pneumococcus alive and virulent is 

 to receive the infected blood of an inoculated animal into 

 a small glass tube 5 mm. in diameter and 20 cm. long, so 

 that the blood completely fills the tube, which is then 

 sealed and kept away from the light at the ordinary tem- 

 perature. If inoculated on to ordinary gelatin, which is 

 then kept in the blood heat (37 C.) incubator, the organism 

 retains its vitality for a month or six weeks. 



Under cultivation the S. pneumonice usually assumes 

 the form of a short streptococcus (Plate XVI. b) (included 

 by Gordon in his S. brevis class) and the capsule is lost. 



