BLOOD GROUPS, HETEROGENETIC ANTIGENS 497 



ditions, may serve to distinguish between individuals, and inasmuch as these 

 characteristics have a genetic basis, they might in a limited way even indicate 

 certain relationships between individuals. But they would not, therefore, 

 become identical with individuality differentials. The four primary blood- 

 group differentials are essentially tissue differentials, which have however 

 certain characteristics in common with the individuality differentials while 

 they differ from the latter in other respects; but the larger the number of 

 accessory blood-group differentials which are added to the primary group, the 

 greater will, in all probability, become the similarity between blood-group 

 and individuality differentials. 



(2) Some authors have identified the blood-group differentials with the 

 constitutional characteristics of a certain individual. The constitution of an 

 individual means an inherited or acquired constellation of structures which de- 

 termine his characteristic modes of reaction or tendencies, including those of 

 an abnormal kind. These inherited or acquired modes of reaction or tendencies, 

 as a rule, become manifest only in their interaction with variable factors of the 

 inner and outer environment. The emphasis is laid in this definition of con- 

 stitution on the reaction-modes ; but constitution may also mean that a certain 

 reaction-mode of an organism is associated with a specific inherited habitus or 

 structural feature, and in this case tne emphasis is laid on the structural 

 aspect. Only in the sense that the blood-group differentials are an inherited 

 characteristic may they be considered as part of the constitution, without, 

 however, representing the whole or even the essential features of the con- 

 stitution. Probably because of the readiness and sharpness with which the 

 blood-group differentials .can usually be determined in human beings, and 

 because of the role they play in blood transfusion and because of the in- 

 herited differences in their distribution among different individuals were they 

 considered as specially representative of the constitution of individuals or 

 races. However, there is more justification for the belief that the various 

 kinds of organismal differentials represent to a much higher degree the con- 

 stitution of an individual, or a race, or of a species, than do the blood-group 

 differentials. 



(3) Individuals and species may have special genes or gene combinations in 

 common which determine the formation of special differentials and antigens 

 as revealed by serological methods. The latter indicate particular relation- 

 ships between these individuals and species or they can be used as a means 

 of distinguishing between these individuals and species. The main problem 

 which we have discussed in this chapter concerns the connection between 

 such special differentials and the organismal and in particular the individual- 

 ity differentials and the relationships which the various differentials have to 

 one another which may render them significant in the analysis of individuality. 



