THE MENINGOOOOOtfS 243 



are < . >iin-\\ hat restricted u^ar with an admixture of serum 

 or blood (preferably human) is most suitable (p. 43). Strains 

 separated in different epidemics appear to present slight 

 individual variations, but the following description may be 

 taken as summing up the common characters: Growth takes 

 place best at the temj>erature of the body, and practically 

 (t-ases at 25 C. On serum agar the colonies are circular discs 

 of somewhat transparent appearance, and possessing a smooth, 

 shining surface ; they have little tendency to become confluent. 

 When examined under a low magnification the colour is seen to 

 be somruliat yellowish, and the margins usually are smooth 

 and regular, though on 



some media slight crena- " ^ 



tion may appear. The '-.*** 



colonies may be of con- 9 * % 



siderable size, reaching *' . "'*""* **t, 



sometimes a diameter of * " * ./, * . * k 



2 to 3 mm. on the third * ." ' ' 



day. On plain agar the *t 



colonies are very niudi * j% ** ' 



smaller, and sometimes * 



no growth occurs; sub- - 



cultures esi>ecially often 



fail to give any growth * ^ * t 



on this medium. In N * ^ *. j .. 



serum bouillon the organ- /"* > *" 



ism ]>roduces a general 



turbidity with formation Vu;. 71. Pure. culture of <liplococcus intra- 



of some deposit after a '-fllulsiris, sliowiiiK involution forms. 



day or two. It ferments 



maltose and dextrose with acid production, a pro}>erty which 



distinguishes it from the micrococcus catarrhalis (vide infra). 



Fermentation tests are most satisfactorily carried out by means 



of solid serum media containing 1' per cent, of the sugar to be 



tested (p. 80). In all cases growth occurs best when the 



medium ha- a neutral or very slightly alkaline reaction. In 



cultures the organism presents the same appearance as in the 



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



tendency to the production of involution forms (Fig. 71), many 



of the cocci becoming much swollen, staining badly, and after- 



wards undergoing disintegration. This change, according to 



Flexner's observations, would api>ear to be due to the production 



of an autolytic enzyme, and he has also found that this substance 



has the property of producing dissolution of the bodies of other 



