484 A MANUAL OF BACTERIOLOGY 



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 cloudiness ; it does not grow on potato. The 

 pneumococcus ferments glucose, lactose, sucrose and 

 raffinose with acid production only, but not salicin 

 and mannitol. Milk is usually curdled, and Hiss's 

 medium (p. 347) with inulin is generally fermented 

 and coagulated ; most other streptococci fail to fer- 

 ment 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 

 alkaline 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 rabbit blood, placed in the 

 incubator for twenty-four hours to prove sterility, inocu- 

 lated, capped, and kept at 37 C. The pneumococcus also 

 grows well on Fleming's media (see " Influenza "). 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 (Klein). 



Under cultivation the S. pneumonic^ usually assumes 

 the form of a short streptococcus (Plate XVII, b) (in- 

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

 lost, but is regained on passage through a susceptible 

 animal, or by growing in fluid serum. A good deal of 

 variation occurs in the morphology of the organism 

 obtained from different sources and under cultivation. 

 The thermal death -point of the S. pneumonice is 53 C., 

 the time of exposure being ten minutes, and it is readily 

 destroyed by the ordinary germicides, by light, and by 

 desiccation ; but in dried sputum it may retain its 

 vitality and virulence unimpaired for weeks. 



