752 PASSIVE IMMUNIZATION SERUM THERAPY 



5. The operator must then choose between the median or lateral 

 route of puncture. The median is the easier, and should always be 

 adopted by the inexperienced operator. 



Wash off the iodin with a pledget of cotton soaked in alcohol. Lo- 

 cate the chosen interspinous space, pressing well between the spines 

 with the left thumb or index-finger, and holding the finger in place pass 

 the needle perpendicularly in the median line between the spines, or, 

 better still, at an angle of 45 degrees upward and inward. If an ob- 

 struction is felt, withdraw the needle slightly and pass it in a different 

 direction until it imparts a sense of " giving way," which indicates that 

 the subarachnoid space has been reached. Quincke has estimated the 

 depth of lumbar puncture in adults to be usually from 4 to 6 cm. ; in 

 large muscular men it is from 7 to 8 cm., and in fat persons, about 10 

 cm. 



The needle should be inserted slowly and deliberately, rather than 

 quickly, as puncture of a bone is likely to be followed by a dull, aching 

 pain, and, indeed, the point of the needle may be bent or broken. 



The fluid may fail to flow or flow very slowly. This may be due to 

 the presence of a thick exudate, impalement of a nerve filament, or ad- 

 hesions arising from a previous puncture. The needle may be turned 

 gently or the trocar inserted to remove an obstruction, after which the 

 flow usually starts; if it does not do so, the needle may be withdrawn 

 slightly or cautiously inserted a little further. 



6. Fluid is collected in the centrifuge tubes while blood-pressure 

 readings are being made. When the pressure drops 10 mm., or if the 

 flow is about a drop every three or five seconds, the tubing is connected 

 and the serum injected very slowly. 



As a general rule, as much fluid should be withdrawn as can be done 

 with safety, and the maximum dose of serum given. When the flow is 

 scanty, a larger dose of serum may be given than counterbalances the 

 fluid removed, the injection being guided by the blood-pressure. When 

 the total drop reaches 20 mm. of mercury, the injection should be dis- 

 continued, or if continued, the patient should be watched closely for 

 other symptoms of collapse. 



7. After the injection has been completed the needle is quickly with- 

 drawn and the wound covered with sterile gauze held in place by ad- 

 hesive straps. All iodin should be washed off with alcohol to avoid irri- 

 tation or an actual dermatitis. 



Syringe Method. 1. The technic is practically the same as that 

 just described, except that the injection is given with a syringe. 



