THE MENINGOCOCCUS 289 



almost or quite clear, almost free from cells, and the cocci 

 may be very scanty. In cultures the organism occurs as 

 cocci, diplococci, and occasionally as tetrads. Swollen 

 involution forms may appear, and the cocci of different 

 strains may vary in size. 



Cultural characters. The meningococcus is an obliga- 

 tory aerobe, and does not usually grow at a temperature 

 below about 23 C. It will not grow on ordinary agar or 

 in broth, and many special media have been devised for 

 its cultivation. One of the best is blood-agar, or ordi- 

 nary agar smeared with blood, human or rabbit. Serum 

 or ascitic -fluid agar or broth are also good soils. Nutrose 

 ascitic agar (" nasgar ") was formerly recommended by 

 Gordon, but has not fulfilled expectation : 



Ascitic fluid . . . . . 15 c.c. 



Distilled water 35 c.c. 



Nutrose ....... 1 grm. 



The mixture is placed in a flask, brought to the boil with con- 

 stant shaking, and filtered. It is then mixed with double the 

 volume of ordinary nutrient agar, steamed for thirty minutes, 

 filtered, and filled into tubes. 



Gordon and Hine have devised another medium legu- 

 min trypagar made with Douglas's trypsin agar with the 

 addition of a saline extract of pea-flour and preferably 

 also of some serum. It is quite a good medium, though 

 not so good as blood agar, but has the advantage that it 

 can be made in any quantity and stored for use. 



The saline extract of pea-flour is prepared by taking 

 100 grams of pea-flour (Pearce Duff's), 100 grams of salt 

 and 1 litre of distilled water. The mixture is steamed 

 for half an hour, allowed to settle, and the extract filtered. 

 Five per cent, of this extract is added to trypagar. 



The colonies of the meningococcus on blood or legumin 

 agar after twenty-four hours' incubation at 37 C. appear 



M.B. 19 



