AGGLUTININS 75 



reaction are 1 in 40 and 1 in 80. The dilutions are 

 conveniently made in small test-tubes or watch-glasses. 

 For the 1 in 40 dilution, one drop of serum is placed 

 in the test-tube or watch-glass by means of the pipette, 

 and 19 drops of distilled water are then added with 

 the same pipette. This makes a 1 in 20 dilution of the 

 serum, a platinum loopful of which added to a loopful 

 of bouillon typhoid culture gives the desired 1 in 40 

 dilution. Similarly for the 1 in 80 dilution, one drop 

 of serum and 39 drops of water are mixed in a test- 

 tube, making a dilution of 1 in 40. A loopful of this 

 together with a loopful of typhoid culture gives the 1 

 in 80 dilution. This is the most reliable method of 

 preparing the patient's serum, as it is free from red 

 cells, and the dilution is accurate. 



(2) By means of a leucocyte counting pipette: 

 The blood is di-awn up into the leucocyte counting 

 pipette of the Thoma-Zeiss apparatus, as far as the 

 0.5 mark, just as for a leucoc}i;ic count. Instead of 

 the acetic acid used in the latter procedure, however, 

 the tube is filled up to the 11 mark with distilled water, 

 thus immediately giving a dilution of 1 in 20. This 

 is the most rapid method of preparing the patient's 

 blood, and works very satisfactorily in hospital prac- 

 tice, where the test is usually carried out immediately 

 lafter collection of the blood. The red cells interfere 

 very little, if any, with the reaction. 



