102 CLINICAL BACTERIOLOGY AND HjEMATOLOGY 



standardizing of the materials is more difficult, and is of vital 

 importance. 



Preparation of the Emulsion of Corpuscles. — This has been already 

 described. They should be washed at least three times, using 

 normal saline containing citrate of soda (to prevent coagulation), 

 the first time, plain normal sahne (preferably sterile) subsequently. 



The Amboceptor. — The preparation of this material requires a 

 vivisection licence, and the serum must be purchased. It is 

 advisable to test it with normal serum just as the antigen was 

 tested. Thus, a series of preparations of normal serum, the 

 (a) tube containing i part of normal serum + 4 parts of 

 normal saline, the {h) tube containing i part of normal serum 

 + 4 parts of good antigen, diluted i in 10, should be incubated, 

 and then i unit of a mixture of i part of red corpuscles and 

 4 parts of the amboceptor serum to be tested should be added 

 and stirred occasionally. There should be complete haemolysis 

 in the first tube, nearly complete haemolysis in the second. Too 

 weak a serum will give an apparent positive result with many 

 normal sera : some complement is absorbed by the antigen, and 

 not enough is left to haemolyze the partially-sensitized corpuscles. 

 Such amboceptor serum is quite useless and misleading. 



Apparatus. — I greatly prefer the special incubator that Messrs. 

 Hearson have made for me, as the tubes stand in a water-bath, 

 and so are brought almost instantaneously to the requisite tem- 

 perature (see Fig. 24). A similar tray is inserted in the incubator 

 referred to on p. 20. The test can be carried out quite well in 

 an ordinary incubator, but the incubation must be longer (ten 

 to fifteen minutes). If this is done, it is convenient to stick the 

 tubes side by side on a slip of wood or a box-Hd covered with 

 plasticene, a substance that is of use in a variety of ways in the 

 pathological laboratory. 



The test-tubes should be about ^ inch in internal diameter and 

 2 inches long. They can be procured or easily prepared from 

 suitable glass tubing. 



The only other piece of apparatus is a pipette, such as is used 

 for opsonic work, the Widal reaction, etc. It should not be too 

 wide (so as to avoid waste of material), and a unit mark should 

 be made about | inch from the tip. Then take 4 of these 

 units of water or other fluid, expel them into a watch-glass, and 

 suck the 4 into the pipette so as to form a continuous column. 

 Make a mark to indicate the point to which this column reaches 



