LUMBAR PUNCTURE 155 



Of these, the organisms which are most likely to occur are : 



The tubercle bacillus 1 .■ , , 



Meningococcus } accounting for about 90 per cent, of cases. 



The pneumococcus. 



Streptococci and staphylococci in secondary cases due to spread from 

 ear, etc. 



And this shows roughly the order of frequency. 



Preparation of Films. — If the fluid is thick and purulent, films 

 should be prepared, dried, and fixed in the ordinary way. If the 

 fluid is thin and watery, it should be centrifugalized or allowed 

 to stand for some hours. A certain amount of coagulation will 

 take place, and the sediment which collects will contain the bulk 

 of micro-organisms. The clear fluid should be poured off and 

 used for testing chemically, and the sediment used for the pre- 

 paration of films, of which several will be required. The subse- 

 quent examination will depend to some extent upon the nature of 

 the organism which is probably present ; for general purposes 

 stain one or more films with Lofiler's methylene blue (two 

 minutes), wash, dry, mount, and examine. 



Streptococci and staphylococci will be readily recognized by 

 their morphological characters. If diplococci are present they 

 may be pneumococci, Weichselbaum's diplococci, or gonococci. 

 Stain a film by Gram's method and counterstain in dilute carbol 

 fuchsin in the method described for the gonococcus. Pneumococci 

 will retain the violet stain, while Weichselbaum's organism and 

 gonococci will be coloured red. 



Weichselbaum's Diplococcus meningitidis intracellularis is the 

 specific cause of cerebro-spinal fever. It is a diplococcus which 

 varies very considerably in size, but is usually rather smaller than 

 the gonococcus. The opposed surfaces of two cocci making up 

 the pair are usually somewhat flattened, but this is not so marked 

 as in the latter organism. It is often contained within the poly- 

 nuclear leucocytes, but is not grouped in large numbers in a single 

 cell — others being free — as is usually the case with the gonococcus 

 (see Plate III., where the two organisms are contrasted). The 

 two also differ in their cultural characters and in their patho- 

 genicity to animals. If any question should arise as to which of 

 the two is present in the meningeal exudation in a case in which 

 no cultures have been taken, other evidence of gonorrhoeal infec- 

 tion should be sought for. 



Still's diplococcus of posterior basic meningitis cannot be 



