MICROCOCCUS INTRACELLULARIS MENINGITIDIS 543 



is a matter of judgment. Every bacteriologist confronted with the 

 problem should immediately plant plates of the medium which he 

 is going to use, with spinal fluid or with cultures recently isolated, 

 and familiarize bimself with the colonies on this medium, at various 

 stages of growth. In spite of our not inconsiderable experience, we 

 would do this ourselves. Plates that are too thickly covered with 

 'colonies are of no use. 



On blood medium, the true meningococcus colonies do not produce 

 any change in the blood. They are slightly translucent and look 

 somewhat stringy. They are homologous and slightly glistening. 

 They are practically indistinguishable from young colonies of M. 

 Flavus which is also a Gram-negative diplococcus, but which is easily 

 distinguished subsequently by the fact that it will grow at and 

 below 25 C., produces a yellow pigment on further cultivation, and 

 has a tendency to agglutinate spontaneously in normal horse serum. 



Having ringed the suspicious colonies, some of them are now 

 picked and stained by Gram. Our habit is to take up part of a 

 colony which we strongly suspect of being meningococcus, plant part 

 of it immediately, and from the rest make the Gram stain, since 

 plating after taking material for Gram stain may increase the 

 chances for contamination. This point, however, is not of very great 

 importance. 



The suspicious colonies are now planted upon blood agar slants, 

 the medium being made up as for the plates. These slants should 

 not be used directly from the ice-box, but should be warmed. Dried 

 media must not be used. 



If two tubes can be inoculated, one should be kept at room 

 temperature. Growth in the incubator for about twelve hours gives 

 sufficient growth for further identification. 



Gram stains are now made from the tubes. 



If the morphological and staining properties are proper, agglu- 

 tination is carried out. 



Diagnostic Agglutination. The organisms are emulsified in 

 isotonic salt solution. Agglutination may be done against type sera, 

 or against polyvalent serum. When large numbers of cases are 

 examined, as in times of epidemic, it is best first to agglutinate 

 in polyvalent serum, preferably one in which the agglutinin titre 

 for a great many different meningococcus strains has been con- 

 trolled. As a general rule, the polyvalent sera used in this country 

 will show specific agglutinations for practically all meningococcus 



