BLOOD GROUPS 51 



puscles adhered to each other and formed ckmips that under the 

 microscope looked something hke bunches of grapes. (See Fig. 1-2, 

 p. 3). In strong reactions all the red cells in the preparation stuck 

 together, leaving a clear supernatant fluid. Landsteiner showed that 

 this behavior could be explained by assuming that there may be two 

 reactive substances in the erythrocytes and two corresponding anti- 

 substances in the plasma which react with the erythrocyte substances. 

 The substances in the erythrocytes have been shown to be antigens ; 

 they are also called isoagglutinogens. The substances in the plasma 

 or serum which combine with them and thus cause agglutination have 

 all the properties of agglutinating antibodies, and are called isoagglu- 

 tinins. 



It is obvious that the substance in the plasma which combines 

 with the erythrocytes of another individual and causes them to ag- 

 glutinate could hardly coexist in the same blood stream with the 

 corresponding agglutinogen ; for, if it did, an individual's plasma 

 would agglutinate his own erythrocytes. The rule, first stated by 

 Landsteiner and known by his name, is that those agglutinins will 

 be present which can coexist with the agglutinogens present in the 

 cells. The agglutinogens, called arbitrarily A and B, can be present 

 in the cell singly or together, or can both be absent. This gives us 

 the combinations of the four classical blood groups. (Table 4-1). 



Landsteiner's discovery explained why transfusions of blood from 

 one individual to another had previously only occasionally been suc- 

 cessful. If a blood donor is selected at random, the chances of obtain- 

 ing one whose blood group is compatible with that of the recipient 

 are not good. It was only when pretransfusion blood grouping be- 

 came a routine that l:)lood transfusion became a safe and reliable 

 procedure. 



TABLE 4-1 

 The Landsteiner Blood Groups 



Blood group Antigens in cells Agglutinins in plasma 



