stout: pollinations in cichorium intybus 429 



'14, p. 229), and the agglutinative characteristics of various 

 bacteria may be modified by life in different hosts (Smith and 

 Reagh '04; Zinsser '14, p. 231). The quite general application 

 of the principles of agglutination, however, suggests that similar 

 reactions may be involved in compatibilities and incompatibilities. 

 The appearance of agglutination reactions between the blood 

 cells and the sera of different animals of the same species or strain 

 (isoagglutination) suggests that at least in the higher animals 

 types of antigen incompatibility may exist between closely related 

 individuals. Such reactions have been studied especially in man, 

 and it has been found (Ottenberg '11) that, in respect to the 

 isoagglutination reactions between sera and red blood cells, indi- 

 viduals fall into four classes: class I, serum will agglutinate red 

 cells of all members of all other groups, but the red cells of indi- 

 viduals of the group are not agglutinated by the serum of any 

 individual of any class; class II, serum agglutinates in classes III 

 and IV only, and red cells are agglutinated by serum of classes 

 I and III only; class III, serum agglutinates in class II and IV^ 

 only and blood cells are agglutinable by sera of classes I, II, and 

 IV: class IV, serum will not agglutinate red cells of any class and 

 has red cells that are agglutinable by every other class. These 

 reactions within and between the four groups have been explained 

 by the assumption of two pairs or sets of reacting substances; 

 two different active substances (agglutinins x and y), and two 

 different agglutinable or sensitive substances (X and Y). The 

 agglutination reaction is assumed to occur only when the two 

 bloods that are mingled bring together at least one pair x and X 

 or y and Y. Between bloods of members of any one class there 

 is no incompatibility in the form of agglutination. The reciprocal 

 interactions between members of classes I and II, I and III, 

 I and IV, II and IV are different. Two reciprocal pairs, II 

 with III and III with IV, give the same reaction. Also indi- 

 viduals of the first class constitute about 50 per cent of all persons 

 examined, and members of the fourth class are relatively rare. 

 Members of the third group especially often show individual 

 irregularities and deviations from the rule which it is assumed 

 involves the presence of another substance, called hemolysin, 

 which exhibits very sporadically the condition of activity or 

 latencv. 



