480 THE BIOLOGICAL BASIS OF INDIVIDUALITY 



differentials ; it is not sufficient that certain structural or functional peculiari- 

 ties should serve as distinguishing marks between different individuals or 

 species, but a correspondence between the constitution of the organismal 

 differentials and the genetic relationship of the organisms is required in 

 addition. As we have seen, the sum of certain organ or tissue differentials, or 

 even a single characteristic feature of a certain kind, may serve to distinguish 

 different species as well as different individuals, but these individual organ 

 and tissue differentials do not become thereby organismal and individuality 

 differentials. Thus the ridge patterns of the skin, the scents and many other 

 peculiarities, which are not individuality differentials, allow the differentiation 

 between different individuals. 



If we keep these criteria of the organismal differentials, and in particular 

 of the individuality differentials, in mind, the differences which exist between 

 blood-group differentials, their agglutinogens, and the organismal differen- 

 tials are obvious. The primary blood-group differentials allow the separation of 

 individuals into four groups, irrespective of their relationship. Two brothers, 

 members of the white race, may belong to different blood groups, while one of 

 the brothers and a member of an African race, or even an anthropoid ape, 

 may belong to the same group. Thus the difference between individuality 

 differentials and the differentials of blood groups is evident. Even the differen- 

 tiation of individuals by means of the four primary blood groups is impossible 

 as a general rule, although in certain cases they may help in identifying per- 

 sons and even in establishing relationships to other persons ; they resemble 

 in this respect other hereditary organ characteristics, which may also be used 

 for this purpose. 



For the identification of the blood-group differentials we have at our dis- 

 posal : ( 1 ) The various specific agglutinins normally present in human sera ; 

 and (2) the specific immune agglutinins which are produced by injecting, 

 into rabbits, human blood corpuscles possessing a certain group differential, 

 these immune agglutinins being absorbed in a specific manner by the ag- 

 glutinogens (group differentials) to which they are adapted. Either the cor- 

 puscles as such, or alcohol extracts of the particular group of erythrocytes 

 which contain the specific group differentials, are used for absorption. By these 

 means we can determine also the occurrence of similar differentials which 

 function as agglutinogens in blood corpuscles of various species of animals, or 

 we may study the relationship of the blood-group differentials to other differ- 

 entials, as for instance, the Forssman differentials. 



The same principle applies to the analysis of the Forssman heterogenetic 

 differentials, although in this case hemolysins, and in particular those dis- 

 solving sheep corpuscles, are used instead of agglutinins. Guinea pig or horse 

 kidney, as bearers of the Forssman differentials, serves as tissue with which 

 other material may be compared. In using these methods for the analysis of 

 the identity or lack of identity between different kinds of differentials, we find 

 that while certain differentials behave in every respect like the typical blood- 

 group differentials, other differentials do so only in an imperfect manner. Re- 

 sults of this divergent kind are obtained especially when we study the blood- 



