ESTIMATION OF THE OPSONIC CONTENT OF THE BLOOD 221 



Preparation of the Patient's Serum. A small amount of blood 

 (about 6 or 8 drops) is collected in a little tube like the one pictured 

 in Plate III at b, by puncturing the lobule of the ear at its free margin, 

 in the usual manner, and dipping up the blood as it is milked out 

 by moderate pressure. The little tubes measure about two inches 

 in length and have a diameter of one-quarter of an inch; they may 

 be closed with a little stopper or with adhesive plaster, and can 

 then be readily transported. The blood is allowed to clot, the 

 coagulum separated from the \valls of the tube by means of a plati- 

 num wire, and the specimen centrifugalized until the corpuscles have 

 been packed down and well separated from the serum. 



In place of the tubes just described, which are really most con- 

 venient, Wright employs special capsules like the one pictured in 

 Plate III at c, both ends of which are sealed. The blood is collected 

 by puncturing the thumb near the root of the nail, after having 

 previously allowed the arm to hang down and then applying some 

 constriction behind the distal joint (tape, rubber tubing). The 

 puncture is made with the sharp point (s) of the straight limb of the 

 capsule. The sealed tip (ra) of the bent limb is knicked off and the 

 open end held to the exuding drop of blood which enters by capillary 

 attraction until it reaches the mark n. After knicking off the sealed 

 tip at s, the capsule is inverted, when the blood will occupy the 

 space above s. The aperture at s is again sealed, and the serum 

 now separated from the corpuscles by centrifugation, to which end 

 the capsule is suspended on the rim of the centrifugalizing tube by 

 the bent limb. In the end the tube is cut with a file at n. 



Preparation of the Normal Control Serum. This is collected in the 

 same manner as the patient's serum and separated from the corpus- 

 cles by centrifugation. It is best to pool three or four normal sera, 

 viz., to mix equal quantities from three or four individuals. If, 

 however, the serum of one single person (the experimenter, for 

 example) has been thoroughly studied and always found normal, 

 this single serum may suffice for ordinary purposes. Women during 

 menstruation, hard workers, and individuals who are pale and below 

 weight, even if otherwise healthy, should not be taken as pontrols, 

 nor even included in a pool. Occasionally, apparently normal 

 individuals are also encountered, who habitually have a higher 

 opsonic content than normal, and such must, of course, also be 

 excluded. The process of digestion further tends to increase the 



