544 



VERTEBRATE LIFE AND ORGANIZATION 



233. Blood Groups 



When the practice of transfusing blood from one person to another 

 was begun, it was found that the transfusions were sometimes successful, 

 but more often they were not and the erythrocytes in the blood of the 

 recipient would clump (agglutinate) with fatal results. Careful analysis 

 by Landsteiner at the begmning of this century showed that specific 

 antigenic proteins, called A and B, might be present within the erythro- 

 cytes. These antigens are called agglutinogens since they may cause 

 agglutination of the red cells. Some individuals have protein A, some 

 B, some both A and B, and some neither. Antibodies (agglutinins) 

 specific for these agglutinogens, and designated a and b, may be present 

 in the plasma. If an individual whose plasma contains agglutinin a 



should receive blood from another whose erythrocytes contain agglutino- 

 gen A, an antigen-antibody reaction occurs, and the erythrocytes ag- 

 glutinate. 



Four main groups of persons can be recognized, according to the 

 presence or absence of these agglutinogens and agglutinins (Table 5). 

 Blood containing a certain agglutinogen does not, of course, contain 

 the agglutinin specific for it. It it did, it would agglutinate itself. Trans- 

 fusions between members of the same group are perfectly safe, and 

 transfusions between different groups are also safe provided that the 

 donor's erythrocytes do not contain an agglutinogen that will react with 

 the recipient's agglutinins. The agglutinins in the donor's plasma be- 

 come so diluted in the recipient that they have no effect and they may 

 be disregarded unless an unusually large transfusion is given. Members 

 of Group O, who have neither of the agglutinogens, can give blood to 

 members of any group and are "universal donors." But since their 

 plasma contains both of the agglutinins, they can receive blood only 

 from members of their own group. Members of Group AB, in contrast, 

 have neither agglutinin, and can receive blood from members of any 

 group. Since they have both agglutinogens, they can give blood only to 

 members of their own group. They are "viniversal recipients." Members 

 of Group A and B can give blood to members of Group AB and receive 

 from members of Group O. The inheritance of these blood groups is 

 considered in section 282. 



