THE TECHNIQUE OF SERUM REACTIONS 315 



The tests may be done in a number of different ways; the most 

 easily carried out, however, is the so-called slide agglutination which 

 was introduced during the war. 



In order to properly type an unknown blood, sera from group 

 II and III should be available. A drop of each of these sera is 

 put upon a slide and the corpuscles of the unknown blood added 

 either in the form of a fraction of a drop of the blood taken directly 

 from the finger or ear of the subject, or, better, a fraction of a drop 

 of defibrinated blood or blood taken into about twice its volume 

 of salt solution or sodium citrate solution. The preparation of the 

 blood to be tested is so simple that nothing further need be said. 

 The corpuscles so obtained are mixed with the types of sera of 

 types II and III. By referring to the table it will be easily seen 

 that, if: 



The blood agglutinates in neither of the sera, the subject belongs 

 to type IV. 



If the cells agglutinate in type II, and not in type III serum, 

 the subject belongs to type III. 



If the corpuscles agglutinate in type III and not in type II 

 serum, the subject belongs to type II. 



If the corpuscles agglutinate in both sera, the subject belongs 

 to type I. 



The blood types as described above are among the few serological 

 reactions which are inheritable by Mendelian laws. They are not, 

 however, present in the child at birth. According to recent studies 

 by Unger, only about 25 per cent of new born infants have cells 

 that can be agglutinated. And only about 13 per cent of new born 

 children have isoagglutinins. Incompatibility between mother and 

 child may occur. 



The Determination of Antibodies in Sera by Complement Fixa- 

 tion. The principle of complement fixation, discovered by Bordet 

 and Gengou 11 in 1901, has been utilized both in bacteriological inves- 

 tigations, and in practical diagnosis for the determination in serum 

 of the presence of specific antibodies. The reaction depends upon 

 the fact that when an antigen, i.e., a substance capable of stimulating 

 the formation of antibodies, is mixed with its inactivated antiserum, 

 in the presence of complement, the complement is fixed by the com- 

 bined immune body and antigen and can no longer be found free in the 



11 Bordet and Gengou, Ann. de 1'inst. Pasteur, xv, 1901. 



