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 suvgeon 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 
