PIPETTES 



37 



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 

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

 lobe is well rubbed by means of a piece of hnt, 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), or with the glass needle described below. 

 This is done by a short, sharp "jab," and should not be felt as 



Fig. i8. 

 A, Before coagulation ; B, after, showing clot suspended in clear serum. 



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 pro- 

 cess as often as necessary. There are few patients from whom 



