LUMBAR PUNCTURE. I2Q 



If no fluid flows through the needle it is presumptive 

 evidence against the presence of acute meningitis. A 

 "dry tap" may, however, occur from plugging of the 

 needle with fibrin, or from its point coming in contact 

 with a nerve root (Osier), and in some cases of menin- 

 gitis the purulent exudation is too thick to flow through 

 the needle. 



4. Examination of the fluid. a. Naked eye. When 

 meningitis is present the fluid is always more or less 

 turbid, and some observers hold that the turbidity is 

 greater in proportion to the severity of the case. Osier 

 has pointed out that the fluid may be alternately turbid 

 and clear, being clear during the remissions, and turbid 

 during the exacerbations of the disease. Blood-stained 

 fluid may occur in meningitis or from haemorrhage into 

 the cerebral or spinal meninges apart from inflamma- 

 tion. The presence of clear fluid affords strong evi- 

 dence of the absence of meningitis, but in tubercular 

 meningitis the amount of turbidity may be very slight. 



b. Microscopical. Prepare films of the exudate in the 

 manner recommended on p. 131 if the fluid is thin and 

 watery ; if it is thick and purulent treat it like ordinary 

 pus. Stain by any of the methods recommended 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 lymphocytes (indicated by their small 

 size, large, circular, deeply staining nuclei, and ab- 

 sence of granules) the presumption is that the case 

 is one of tubercular meningitis. In meningitis due to 

 other bacteria the chief cell is the polynuclear leuco- 

 cyte ; this may be recognised by its larger size, 

 its twisted (apparently multiple) nucleus, and, if 



K 



