THE PHENOMENON OF AGGLUTINATION 237 



with the red blood cells of another species. Like the bacterial ag- 

 glutinins, the hemagglutinins are relatively thermostable and are 

 best observed, therefore, after the sera are inactivated. Otherwise 

 rapid hemolysis will often obscure the agglutination. Like other 

 agglutinins the hemagglutinins thus produced are specific, acting 

 only upon that variety of cells which are used in their production. 

 Moreover, certain sera may normally contain hemagglutinins for they"' 

 blood cells of animals of another species. An illustration of this is 

 the hemolytic and hemagglutinating property of normal goat serum 

 for rabbit cells but there are many other examples which might be 

 cited. Such normal hemolytic and hemagglutinating properties for 

 the cells of other animals usually render the sera toxic for these ani- 

 mals, and some observers have attributed the toxicity to this agglu- 

 tinating action, believing that the clumped erythrocytes form emboli 

 around which clotting is initiated. The writer's own investigations, 

 however, seem to show that this is not the case, since the toxicity of 

 such sera is completely removed after they have been heated, in spite 

 of the fact that the hemagglutinative property remains unchanged. 



In discussing hemolysins, also, we called attention to the observa- 

 tion that the sera of animals may develop the property of hemolyzing 

 blood cells of other individuals of the same species when immunized 

 with such cells, and that on occasion such isolysins may be normally 

 present. 



Analogous to iso-lysins, iso-agglutinins also have been observed. 

 They were described first in human blood in 1900, independently, by 

 Landsteiner, 52 and by Shattock. As the result of the work of a 

 number of men, in particular that of Landsteiner, of Ascoli, 53 and 

 of Descatello and Sturlii, 54 it became evident that all human blood 

 fell into four sharply separated and, for the individual, permanent 

 groups, according to the way in which they interagglutinate. The 

 members of the first group have blood cells which are not agglutinated 

 by the serum of any human blood. The serum of the members of 

 this group agglutinates the blood cells of persons belonging to any 

 of the other three groups. This group constitutes between 40 to 50 

 per cent, of all human beings. Members of the second group have 

 blood serum which agglutinates the cells of persons belonging to the 

 third and fourth groups ; while the cells of the second group are ag- 

 glutinable by the serum of the first and third groups. The third is 

 the reciprocal of the second, and the serum of the third group ag- 

 glutinates the cells of the second and fourth groups ; while the cells 

 of the third group are agglutinated only by the serum of the first and 

 second groups. The fourth group (which is very rare) is the recipro- 



52 Landsteiner and Richter. Zeitschr. f. Med., 3, 1902. 



53 Ascoli. Munch, med. Woch., 1901. 



54 Descatello and Sturlii. Munch, med. Woch., 1902, 49, p. 1090. 



