128 BACTERIOLOGICAL DIAGNOSIS. 
Lastly, pour some alcohol on to the skin of the patient’s 
back to wash off the excess of the antiseptic. 
2. Opevation.—Position.—Get the patient (still lying 
on his left side) to draw up his knees so as to flex his 
back somewhat, and to turn partly over on to his face. 
It is scarcely necessary to say that the operator must 
not touch the patient, as his hands have now been 
sterilised. 
Identify the processes of the third and fourth lumbar 
vertebree and mark the centre of the space between 
them by means of the index finger or thumb of the left 
hand. If local anesthesia is to be employed freeze the 
skin round a point about one-third of an inch to the 
right of the middle line, opposite the spot marked by 
your left finger or thumb, Take the needle in the right 
hand, holding it like a pen, and enter it at a point level 
with the centre of the interspace, and 1 cm. (a little less 
than one-third of an inch) to the right of the middle 
line. Direct it forward, shghtly upwards, and slightly 
inwavds, and press it in with a steady and uniform 
pressure ; this must be applied accurately in the axis of 
the needle, or the latter may bend and take a wrong 
direction. 
If the needle strikes against bone withdraw it almost 
completely and push it on again after changing its 
direction slightly. If bone is again encountered it may 
be advisable to try again in the interspace between the 
second and third processes. 
3. Collection of fluid and inoculation of media._-The first 
few drops of fluid which escape may be stained with 
blood; in this case it should be rejected. Allow a few 
drops of the fluid to flow divectly on to the surface of the 
media without touching the glass. Collect also some of 
the fluid (1-4 drachms) in the sterilised empty tube. 
