Tin: M I:\I.\GOCOCCUS 361 



within the polynuclear leukocytes. It never appears within the nucleus 

 and rarely within other cells (Fig. 110). 



Staining. It ,v/i'/i.v with all the ordinary aniline colors, but best with 

 Loeffler's methylene blue. It is, as a rule, readily decolorized by Gram's 

 solution. Some organisms in many cultures are more resistant than 

 others, but none are definitely Gram positive. It is almost certain 

 that the positive cocci which have been described as meningococci 

 are really contaminating organisms. 



Biology. It grows between 25 and 40 C., best at about 37.5 C., and 

 its development is usually scanty on the surface of nutrient agar, but 

 sometimes a few colonies grow quite vigorously. Now and then cultures 

 grow at 23 C. or slightly less. It grows scarcely at all in bouillon, 

 and scantily in bouillon plus one-third blood serum. It develops com- 

 paratively well on Loeffler's blood-serum medium as used for diphtheria 

 cultures, and on blood serum or ascitic-fluid agar. 



Fro. 110 



Diplococcus intracellularis ineiiingitidis. X 1100 diameters. 



Of the usual sugars the meningococcus ferments dextrose only and 

 even this not sufficiently to coagulate the serum media. It grows on 

 5 per cent, glycerin agar as well as on plain agar. 



When grown on nutrient agar or glycerin agar, a tolerably good 

 growth develops at the end of forty-eight hours in the incubator. This 

 appears as a flat layer of colonies, about one-eighth of an inch in 

 diameter, grayish-white in color, finely granular, rather viscid, and non- 

 confluent unless very close together. On Loeffler's blood serum the 

 growth forms round, whitish, shining, viscid-looking colonies, with smooth 

 and sharply-defined outlines; these may attain diameters of one-eighth 

 to one-sixteenth of an inch in twenty-four hours. The colonies tend to 

 become confluent and do not liquefy the serum. From the spinal fluid 

 in acute cases, wliere the organisms are apt to be more abundant, a 

 great many minute colonies may develop instead of a few larger ones. 

 On agar plates the deep-lying colonies are almost invisible to the 

 naked eye; somewhat magnified they appear finely granular, with a 



