290 A MANUAL OF BACTERIOLOGY 



as moist, grey, translucent, circular or oval discs with 

 regular outline ; after a further twenty hours' growth 

 they may attain a diameter of 3 to 4 mm. The colonies 

 never exhibit any yellowish coloration, as do those of 

 some other Gram-negative cocci (see p. 295). 



The vitality of the meningococcus is brief on blood and 

 legumin agar twenty -four to forty-eight hours. In 

 trypsin broth with the addition of a little serum the 

 meningococcus will live for two to three weeks at 37 C. 

 Vines employs a starch medium consisting of beef -broth 

 with the addition of 1 per cent, starch and 1-5 per cent, 

 agar ; stab -cultures (but not surface cultures) in this 

 medium kept at 37 C. live for two, three or even four 

 weeks. 



Absence of growth at and below 23 C. has been re- 

 garded as a valuable diagnostic feature of the meningo- 

 coccus. Gordon found that of thirty-five strains thirty - 

 two did not grow at this temperature in ten days ; the 

 remaining three showed some growth on legumin agar in 

 forty-eight hours. 



The meningococcus is exceedingly intolerant of cooling 

 and drying ; desiccation kills it in two to five minutes. 

 Hence swabbings for culture from carriers should be 

 inoculated on the spot and the cultures be kept warm 

 until placed in the incubator. 



Small quantities of nasal mucus enhance the growth of 

 the meningococcus, while saliva has a contrary effect. This 

 inhibitory action of saliva is due to the salivary bacteria, 

 chiefly streptococci. 



Fermentation Reactions. These are best obtained in 

 liquid media tinged with litmus and containing 1 per 

 cent, of the fermentable substance, e.g. Hiss's medium 

 (p. 347) or veal broth with some added serum. The 

 meningococcus forms acid from glucose, maltose and man- 

 nose, but not from lactose, galactose, saccharose, inulin, 



