PRACTICAL APPLICATIONS 371 



Meningococcic Infections. 



Very little is known concerning the toxin of the meningococcus. 

 Cultures are of very feeble toxicity for animals, and large doses 

 of the vaccine are usually (though not invariably) well tolerated 

 by human patients. It is probably an endotoxin which is only 

 produced under certain conditions. Its effect in the human 

 subject is mainly a local one, manifested chiefly on the tissues in 

 or near which the cocci are localized. The disease is in most 

 cases a local one, the organism being rarely found in the blood 

 or organs other than the brain and cord. 



The frequency with which the organism is found within the 

 polynuclear leucocytes would lead us to believe that the organism 

 is combated in the main by phagocytosis ; and this is confirmed 

 on the whole by the results obtained by a study of the disease by 

 Wright's method. When opsonic determinations are made using 

 a virulent culture, such as one derived from the patient himself, 

 it is found as a rule to be taken up very badly in preparations 

 made with normal serum and leucocytes, and very well when 

 some of the patient's serum is present, so that very high indices 

 are obtained. This is obviously because the cocci have become 

 animalized, like the virulent pneumococci studied by Rosenow 

 and others. They require a large dose of opsonin, such as is 

 present in serum from a patient who is attempting to combat the 

 disease, and not in that from a normal person. The result is 

 that the opsonic index of these patients is often extremely high, 

 figures of 10 or more being common, and 40 has been recorded. 

 Houston has pointed out that old laboratory cultures which have 

 lost their virulence are phagocyted more easily in presence of 

 normal serum, so that the opsonic index of meningitis patients, 

 as determined by the use of these non-virulent cultures, is com- 

 paratively low. Houston has proposed this test for distinguishing 

 between the "true" meningococcus and allied cocci of similar 

 morphological characters. He determines the opsonic index of a 

 patient suffering from true cerebro-spinal meningitis against a 

 normal control, using both a known meningococcus culture and 

 that under consideration. In what he terms the positive reaction 

 there is, in the case of the normal blood, very little phagocytosis, 

 and no agglutination of the cocci which are not ingested, whilst 

 with the blood from the cerebro-spinal case there is much phago- 

 cytosis and marked clumping of the free cocci. It would seem, 



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