BLOOD GROUPS, HETEROGENETIC ANTIGENS 479 



tion of the red corpuscles of a certain species into a rabbit induces in the 

 latter the formation of hemolysins specifically directed against the corpuscles 

 of that particular species. But it has been found by Forssman that it is possible 

 to produce hemolysins which dissolve sheep corpuscles not only by the intro- 

 duction of sheep erythrocytes into a rabbit, but also by the use of kidney of 

 the guinea pig or of the horse, or of the blood corpuscles of chicken, as anti- 

 gens; if extracts of such cells or tissues are injected into rabbits, hemolysins 

 for sheep corpuscles will be found to circulate in the rabbit blood. Similar 

 differentials which may induce the formation of hemolysins for sheep cor- 

 puscles have been found in the tissues of the most diverse species of animals, 

 and even in certain bacteria, without any reference to the relationship of these 

 organisms with the sheep ; but the organs of certain other species, such as the 

 rabbit, do not usually possess such antigens. Accordingly, two classes of or- 

 ganisms are distinguished, namely those which, like the guinea pig, possess 

 Forssman heterogenetic or heterophile differentials, and others which, like the 

 rabbit, usually do not possess such differentials. The term "heterogenetic" is 

 applied, because they are found in species and classes of animals far distant 

 in relationship from the sheep, and even in bacteria. Evidently these sub- 

 stances behave in a very different way from organismal differentials; there 

 is no specific connection between the systematic relationship of these organisms 

 and the presence of the heterogenetic differentials in their cells, although the 

 possession of Forssman antigens may be characteristic of whole genera and 

 families. In addition to the Forssman antigens there exists still another system 

 of heterogenetic antigens, which is shared by bacteria of the hemorrhagic 

 septicemia group and the erythrocytes of many species of birds (Buchbinder), 

 and presumably many other non-related groups have certain chemical charac- 

 teristics in common. In this connection the fact may be recalled that also 

 estrogenic substances occur in the most diverse classes of organisms. 



In order to analyze the relationship of the blood-group and Forssman dif- 

 ferentials to the organismal and organ differentials the following questions 

 must be considered: (1) By what methods is the presence of the blood-group 

 and Forssman differentials determined? (2) In which organs and tissues do 

 these differentials occur? (3) What is the distribution of these differentials 

 among animals and bacteria? and (4) What is the relationship of the blood- 

 group differentials in various animal species to those in man? 



Let us state once more the characteristic features of the organismal and, 

 in particular, of the individuality differentials. In contradistinction to the 

 structure and function of tissues and organs, which differ from one another, 

 there is something common to all these different organs and tissues in the 

 same individual, at least in the higher classes of animals, which differs from 

 the corresponding characteristics in all other individuals. If we consider in 

 addition, classes, orders, genera and species, and strains and family relation- 

 ships, we then find that the various kinds of organismal differentials, includ- 

 ing the individuality differentials, correspond in their graded properties to 

 the graded phylogenetic relationships of these various types of organisms. 

 This latter characteristic is very important in the definition of the organismal 



