BLOOD GROUPS, HETEROGENETIC ANTIGENS 485 



of a common partial antigen in human corpuscles, and in other cells, without 

 respect to the group to which they belong, as well as in certain Shiga bacilli ; 

 and in the latter, in addition, the Forssman antigen is present. There are a 

 number of other differentials which are found in cells of various species, 

 irrespective of their systematic relationship. Thus human corpuscles of Group 

 A have a certain factor in common with erythrocytes of hog, sheep and cattle. 

 Besides, common differentials are present in hog erythrocytes and in the 

 erythrocytes of man, regardless of the blood-grouping of the latter. There are 

 known still other differentials, which different, not phylogenetically related, 

 species have in common, and in all probability a still larger number, unknown 

 as yet, could be added to those which have so far been established. 



All these observations exclude the possibility of identification of these 

 agglutinable factors with organismal differentials, but not the possibility that 

 these various factors, or some of them, may be present among the individuality 

 differentials, or, rather, that the genes representing these factors may be a 

 component part of the gene sets which determine the individuality differentials. 

 This conclusion holds good even if it should be feasible to distinguish all 

 individuals by a study of their blood-group antigens. If we consider that 

 besides the differences already established between human corpuscles, or 

 between the blood sera of human groups, and of certain individuals in these 

 groups, additional differences might be discovered between the red corpuscles 

 of individuals if their reactions with different animal sera were studied, then 

 we can conceive the possibility that, as Landsteiner suggests, in this way the 

 corpuscles of all, or at least a large number of individuals, might be identified 

 and distinguished from one another. Yet, as stated, it would not follow there- 

 fore that the sum of these factors constitutes the individuality differential. 

 This would require that there should be found the same graded relationship 

 between these regular or irregular, often heterogenous group differentials 

 and the genetic constitution of individuals, as can be shown to exist in the 

 case of the individuality differentials. That an individual can be distinguished 

 from other individuals by means of certain characteristics does not, by itself, 

 prove that these characters represent the individuality differentials. We may 

 be able to identify an individual by means of the combination of certain 

 characteristics which are a part of the Mendelian mosaic of this individual, 

 or even by a single characteristic belonging to the Mendelian mosaic. It is the 

 organismal differentials which determine the graded compatibility in the 

 biological sense between two organisms, and especially between two individ- 

 uals of the same species or race, whereas the blood groups and the immune 

 reactions based on such group differentials, which may be common to man 

 and nearly, or even more distantly, related species of animals, do not exert 

 this function as far as known at the present time. We have discussed these 

 problems already in a preceding chapter, where we considered the relation 

 between natural and experimentally produced immune hemolysins in cattle 

 and fowl and organismal differentials, and we concluded that certain relations 

 may exist between these types of substances. However, it may be assumed that 



