134 BACTERIOLOGICAL DIAGNOSIS. 



If no colonies appear on blood-serum or agar at the 

 end of forty-eight hours the case is probably due to the 

 tubercle bacillus or the gonococcus. In some cases of 

 cerebro-spinal fever the diplococci in the exudate are 

 all dead, and cultures remain sterile. 



INTERPRETATION OF RESULTS. 



The discovery of Weichselbaum's diplococcus indi- 

 cates that the case is one of cerebro-spinal fever. The 

 chief importance in making the diagnosis (apart from 

 the fact that it may throw light upon the occurrence of 

 several cases of meningitis within a short space of time 

 by proving the existence of an epidemic) arises from the 

 fact that the prognosis is decidedly better than in other 

 forms of meningitis. 



Meningitis due to the pneumococcus may arise from 

 dissemination from pneumonia or other pneumonic 

 lesion, by spreading from the middle ear, &c., or may be 

 primary. The examination of the exudate throws no 

 light upon this point, and the cause of the infection 

 must be sought for on ordinary clinical lines. 



Tubercular meningitis is proved by the presence of 

 tubercle bacilli in the fluid, and is indicated by sterile 

 cultures, absence of bacteria from the stained films, and 

 predominance of lymphocytes. 



.The other varieties of meningitis do not call for 

 special mention. 



The chief value of lumbar puncture to the surgeon is 

 that it enables him to diagnose a concomitant menin- 

 gitis (which would negative an operation) in cases of 

 lateral sinus thrombosis and cerebral abscess. The 

 fluid usually becomes bloody within twenty-four hours 

 of a fracture of the base of the skull or laceration of the 



