J. R. Learmonth 143 



factors — that displayed by Group II to factor A, and that by Group III 

 to factor B. The corresponding small letter serves to signify the absence 

 of either factor. A therefore corresponds to the a of Von Dungern and 

 Hirschfeld, B to the /8 ; while the conditions non-a and non-/8 of these 

 authors are represented respectively by a and b. 



Technique. 



1. The provision of test sera. In order to assign a particular blood 

 to one of Moss's four Groups, it is unnecessary to have specimens of the 

 serum of each Group. It will be seen from the table on page 141 that a 

 supply of only two sera is essential, viz. those of Groups II and III. The 

 method of determination is shown in the following table (after Moss) : 



Reaction of R. B. C. of unknown to 



Unknown ^ --^ Group of 



blood Group II serum Group III serum unknown 



X + + I 



X Q + n 



X + III 



X IV 



+ = agglutination. 

 =no agglutination. 



It therefore facilitated the work to have available at its commencement 

 a supply of the sera of Groups II and III from an authentic source. 



Since additional supplies of the test sera become necessary, the man- 

 ner of procuring, selecting, and storing these must be briefly considered. 



It is a matter of experience that sera which belong to the same group 

 vary within wide limits in their agglutinating capacities ; and further 

 that the agglutinophilic capacity of the red cells of a given blood, or, in 

 the case of Group IV, of its absence, is no index of the potency of its 

 agglutinin content. In order to obtain the most active Group II and 

 Group III sera, small quantities of the sera of individuals of these 

 groups are tested against washed red cells of individuals belonging to 

 Group III and Group II respectively. Approximately equal quantities 

 of serum and cells are mixed in each case under similar conditions of 

 temperature etc., and those sera which soonest cause agglutination of 

 the washed cells are selected for stock. 



A suitable donor having been found, about 20 cc. of blood are withdrawn 

 with aseptic precautions from a superficial vein of the arm into a sterile 

 receptacle. The blood is allowed to clot, centrifuged in sterile tubes, and 

 the serum pipetted off in quantities of about 5 cc. into rigidly sterilised 

 glass tubes, which are then sealed in the blowpipe, labelled with the 



10—2 



