36 CLINICAL BACTERIOLOGY AND H^MATOLOG^ 



centrifugal machine and centrifugalized. In this way the clot is 

 driven to the bottom and a large crop of serum obtained. 



Since some practitioners seem to have difficulty in collecting 

 the quantity of blood desirable for the opsonic and other tests, a 

 few more notes on the process may be added. I personally prefer 

 to obtain the blood from the ear, and proceed as follows : the 

 lobe is well rubbed__by means of a piece of lint, until it is markedly 

 hyperaemic, and is then punctured on its lower border with a 

 Hagedorn's needle or platino-iridium hypodermic needle (previously 

 sterilized in the flame). This is done by a short, sharp "jab," 

 and should not be felt as pain at all ; I have frequently done it 

 without waking a sleeping child. The needle is then laid down, 

 and if the blood flows out in large drops (as usually happens 

 if the ear has been well rubbed) it is collected without the 

 slightest difficulty, and this is specially likely to be the case if 

 you puncture the ear of the side on which a patient has been 

 lying. If it does not flow readily, take the lobe of the ear 

 between the forefinger and thumb of both hands, and squeeze it 

 gently so that all the blood in the lobe is forced through the 

 puncture, and collect the drop thus formed. When this has 

 been done the lobe of the ear will be full of blood again, and a 

 second drop can be milked out. Repeat this process as often as 

 necessary. There are few patients from whom several pipettes 

 half full cannot be collected from a single slight puncture. 



Many pathologists prefer the finger. In that case an excellent 

 needle can be made by softening a small piece of capillary tubing 

 in the flame and separating the two ends rapidly. This will give 

 two tapering tubes, which can be broken off so as to leave a very 

 sharp point, with which the skin at the side of the nail can be 

 punctured almost painlessly. The ligature is then applied as in 

 the figure, and the patient bends his finger forcibly, squeezing 

 out two or three drops of blood. After these have been collected 

 the bandage must be removed and the hand allowed to hang 

 down, so that the finger refills with blood. It is rebandaged and 

 rebent, and more blood obtained. This process should be learnt 

 since it is the simplest one by which the practitioner can obtain 

 blood from himself, as is often necessary in opsonic work. 



