200 THE COLLECTION OF MATERIAL 



of wounding the nerves since they diminish in number as the canal is 

 descended. 



The transverse width of the third and fourth lumbar spaces is from 

 18-20 mm. and their depth from above downwards 10-15 mm. Their shape 

 varies with age : the fifth space between the last lumbar arch and the upper 

 border of the sacrum is wider than but not quite so deep as the two above 

 and marks the situation of the inferior arachnoidal cul-de-sac, which is a 

 true reservoir of cerebro-spinal fluid. 



The operation is generally performed between the fourth and fifth lumbar 

 vertebrae. An horizontal line drawn between the highest points of the two 

 iliac crests passes through the tip of the spinous process of the fourth lumbar 

 vertebra ; by inserting the needle immediately below this process the space 

 between the fourth and fifth lumbar vertebrae is entered. 



The depth to which the needle must be inserted will depend upon the 

 age and also upon the state of nutrition of the patient ; in a child it will be 

 1'5 cm., 2 cm. and sometimes 3 cm. according to its condition ; in the adult, 

 4-6 cm. If the needle pass too far it may reach the premeningeal venous 

 plexus and cause a slight haemorrhage, in which case the needle must be 

 withdrawn a little before the cerebro-spinal fluid can be collected. 



Operation. 1. Sterilize a platinum-indium needle with a short bevel and 

 a calibre of 0*8-1 mm. and about 5 cm. long for a child and 8 cm. for an 

 adult. 



The needle should have a fine platinum wire passed through it reaching as 

 far as the bevel but not interfering with its cutting edge. 



2. Place the patient in the lateral decubitus on the edge of the bed with 

 the thighs strongly flexed on the abdomen and the legs on the thighs, the 

 head being slightly raised on a pillow and flexed on the thorax. 



The patient may also sit up with his legs hanging over the edge of the 

 bed, the body being bent forward and the back arched. This position, how- 

 ever, though more convenient for lumbar puncture, is often rendered 

 impossible by illness and has the disadvantages of tiring the patient and 

 stimulating muscular reaction. 



3. Asepticize the skin by washing with soap, ether and alcohol. Or. 

 more simply, paint the surface of the skin a few minutes before doing the 

 operation, with tincture of iodine. The surgeon must of course prepare 

 his hands as for any other surgical operation. 



4. Determine the position of the line connecting the highest points of the 

 crests of the iliac bones (vide ante). This line will pass through the upper 

 border of the spinous process of the fourth lumbar vertebra. 



5. Put the tip of the left index finger on the spine of the fourth lumbar 

 vertebra and keep it in that position throughout the operation. Take the 

 needle with the platinum wire in it in the right hand and pass it perpen- 

 dicularly to the surface immediately below the spinous process and very near 

 (not more than 1 cm. away from) the median line, slowly but deliberately 

 into the spinal canal. Direct the needle forwards and a little upwards. 

 The needle will pass through in order, the lumbo-sacral muscles, the ligamen- 

 tum flavum, the dura mater and the arachnoid membrane. As soon as it 

 enters the sub-arachnoid space the liquid will issue from the needle. 



6. Withdraw the platinum wire and collect the fluid in a sterile test- tube. 



7. Collect 5 or 6 c.c. in the case of a child and 10-15 c.c. in the case of an 

 adult. Lumbar puncture is unattended with danger if no more fluid than 

 this be aspirated. Withdraw the needle and paint over the puncture with 

 iodoform and collodion. The patient should remain in bed for 24 hours 

 after the operation. 



