246 EPIDEMIC CEEEBRO-SPINAL MENINGITIS 



best at the temperature of the body, and practically ceases at 

 25° C. On these media the colonies are circular discs with a 

 slightly opaque centre fading into a delicate transparent margin 

 (Fig. 66), and they have a smooth, shining surface ; they have a 

 slightly mucoid consistence and readily emulsify in water or 

 normal saline. When examined under a low magnification the 

 centre appears somewhat yellowish, and the margins usually are 

 smooth and quite regular ; at a later period of growth slight 

 crenation may appear, especially when the medium is somewhat 

 dry. The colonies may be of considerable size, reaching some- 

 times a diameter of 2 to 3 mm. on the second day. A stroke 



• 



Fig. 66. — a. Two-day colonies of the meningococcus on Martin's 

 medium (p. 43), x 9 ; b. the same, in which illumination lias 

 been arranged to show finely granular centre and transparent 

 margin, x 12. Compare with Fig. 69. 



From photographs by Dr. W. B. M. Martin. 



culture gives a broad line of growth of similar character ; the 

 margins tend to be somewhat crenated, and isolated colonies 

 often occur. On plain agar the colonies are very much smaller, 

 and sometimes no growth occurs ; sub-cultures especially often 

 fail to give any growth on this medium. In serum bouillon the 

 organism produces a general turbidity with formation of some 

 deposit after a day or two. It ferments maltose and dextrose 

 with acid production, a property which distinguishes it from the 

 micrococcus catarrhalis (vide infra) ; it has no action on 

 saccharose. Fermentation tests can be carried out by means of 

 either fluid or solid media containing 1 per cent, of the sugar to 

 be tested, along with neutral-red or litmus as an indicator (p. 79). 

 In cultures the organism presents the same appearance as in 

 the body, and often shows tetrad formation. There is also a 



