37 2 MENINGOCOCCIC INFECTIONS 



however, that the test is simply one of the virulence of the 

 culture, rather than that of its specific nature. As regards 

 agglutination, Houston and Rankin point out that this property 

 also is lost on prolonged cultivation on artificial media ; and as 

 regards the behaviour of the coccus in opsonic estimations, exactly 

 the same phenomena are seen when cultures isolated from what 

 are apparently ordinary cases of basic meningitis are tested against 

 the blood of the patient and a normal control. It seems more 

 reasonable to suppose that the coccus from the basic meningitis 

 cases are either of lower virulence, or that their virulence has 

 developed along different lines from a common non-virulent 

 stock, rather than a different species. 



The opsonin present in the serum in meningitis is to a large 

 extent thermolabile. Some thermostable opsonin is present, the 

 amount being roughly proportionate to the height of the index. 



Agglutination is somewhat difficult of study in the case of this 

 organism, owing to the variations presented by different cultures 

 in this respect and the difficulty in procuring a homogeneous 

 emulsion. Tested by ordinary methods, the blood of meningitis 

 cases does not clump in high dilutions : according to Davis, i : 50 

 is about the average. Kutscher states that the phenomenon is 

 much more marked at 55 C., and that a culture which was not 

 agglutinated at all by a specific serum at 37 C. was clumped in 

 twenty-four hours at 55 C. in dilutions of i : 500, or even i : 1,000. 

 If this is correct it may prove important in the clinical diagnosis 

 of the disease, which at present is based mainly on the characters 

 of the cerebro-spinal fluid, and especially on the presence of the 

 coccus. The cytological and chemical examination of the fluid 

 affords definite evidence of the presence of a meningitis, but the 

 cocci are not always discoverable, especially in cases of internal 

 meningitis, or those in which the foramina at the base of the brain 

 are closed. The opsonic index may be of great value, especially 

 if a virulent culture is at hand. According to Houston and 

 Rankin, the positive " reaction " described above is not usually 

 present before the fifth or sixth day in the epidemic form. 



The serum of immunized animals contains a substance which 

 gives the phenomenon of fixation of complement when com- 

 bined with meningococci, and this fact is used by Kolle in the 

 standardization of his therapeutic serum ; but whether this is a 

 bacteriolysin or bactericidal substance is not definitely known. 

 A cording to Davis, normal blood-serum is bactericidal to menin- 



