LUMBAR PUNCTURE I33 



may be very slight. It should be estimated by comparing the 

 fluid with some distilled water in a clean test-tube of the same 

 size in the two cases. 



(b) Microscopical. —Prepare films of the exudate in the manner 

 recommended on p. 135 if the fluid is thin and watery; if it is 

 thick and purulent, treat it like ordinary pus. Stain by any of the 

 methods recortimended for the examination of the blood (Jenner's 

 stain being most convenient), and examine.* 



The presence of leucocytes (except in very small numbers) 

 indicates meningitis. If the bulk of the leucocytes are lympho- 

 cytes (indicated by their small size, large, circular, deeply staining 

 nuclei, and absence of granules) the presumption is that the case 

 is one of tuberculous meningitis. In acute meningitis due to other 

 bacteria the chief cell is the polynuclear leucocyte ; this may be 

 recognised by its larger size, its twisted (apparently multiple) 

 nucleus, and, if the staining method has been appropriate, by the 

 presence in its protoplasm of minute granules which stain with eosin. 

 The fluid may also contain red blood-corpuscles and shreds of fibrin. 



(c) Chemical. — Cerebro-spinal fluid removed from a person who 

 is not suffering from meningitis contains a very minute amount 

 of albumin, while when the meninges are inflamed the quantity 

 is greatly increased. The method of testing these small amounts of 

 albumin quantitatively is hardly within the reach of practitioners ; 

 if a considerable amount of fluid has been obtained, a small 

 quantity should be tested by heat and acetic acid, and the amount 

 of opacity noted. This should be very slight, not more than what 

 would be called a " faint haze " in urinary work. 



Another test which has almost escaped notice, but which I 

 regard as one of the most important, is that for the presence of 

 sugar. For this (as for the testing for albumin) the clear super- 

 natant fluid left after centrifugalization should be used. In health, 

 sugar is present in considerable amount (about o'o6 per cent.), and 

 Fehling's solution is vigorously reduced ; in meningitis, sugar is 

 either reduced to a trace or, much more frequently, completely 

 absent. I have only found this test fail once in about a hundred 

 cases (even in this one the diagnosis was never made absolutely 

 certain) , and regard it as the most certain single sign of meningitis. \ 



* The cytology of the cerebro-spinal fluid is dealt with more fully under the 

 heading of Cyto-diagnosis. 



+ Since writing the above I have met with several cases of tuberculous 

 meningitis in which sugar was present. The reduction of the Fehling is, 

 however, but slight, and the oxide may not appear for several minutes. 



