BLOOD GROUPS, HETEROGENETIC ANTIGENS 495 



only from that of the individuality differentials, but also from that of the 

 accessory blood-group differentials. 



There are found, thus, in human erythrocytes, a number of different differ- 

 entials. We have mentioned the occurrence of species differentials, of the 

 typical blood-group differentials, of the accessory blood-group differentials, 

 of the Forssman differentials, and of certain special differentials which human 

 erythrocytes and erythrocytes of some distant animal species have in com- 

 mon. In addition, we must consider the possibility of the occurrence of organ 

 differentials in various types of human cells. In this connection the observa- 

 tions of Jacobs are of interest. He compared the ability of the erythrocytes 

 of many different species to absorb various kinds of chemicals and he found, 

 on the whole, that the corpuscles of related species resemble each other more 

 in their permeability to and absorbing powers of certain substances than do 

 the erythrocytes from animals more distant phylogenetically, although a 

 strict grading according to phylogenetic relationship is not possible. The red 

 blood corpuscles behave in this respect like some blood-group differentials 

 and characteristics of organs which may show a certain correspondence to the 

 phylogenetic development of these cells and organs. But a gradation in the 

 organismal differentials present in the erythrocytes according to the relation- 

 ship of the various species would also explain this phenomenon. 



This is in all probability a very incomplete list of the differentials oc- 

 curring in erythrocytes and we may assume that besides those named, there 

 occur other differentials. Of special interest for us is the question whether 

 also individuality differentials are present in human erythrocytes. Experiments 

 which we have discussed in an earlier chapter make this very probable. Do 

 transfusion experiments give any indication of their presence? There are some 

 observations concerning injurious results following transfusions of apparently 

 compatible blood which suggest such a possibility ; but other interpretations 

 of these occurrences, such as the presence of an agglutinogen common to 

 man and Rhesus monkey in the blood of the donor, or of an immune ag- 

 glutinin in the blood of the person which received the transfusion, or the 

 presence of agglutinogens A and B in human blood plasma used for intra- 

 venous injection (M. Levine and D. State), cannot be excluded. 



We shall now briefly summarize our conclusions concerning (1) the rela- 

 tions between blood groups and organismal and, in particular, individuality 

 differentials; (2) the relations between blood groups and what is designated 

 as "constitution," and (3) the general significance of the antigens discussed in 

 this chapter. 



(1) The primary blood-group differentials do not make possible a dis- 

 tinction between different individuals in general, but only between some 

 individuals ; they do not indicate the degree of relationship between individuals ; 

 they differ in these and in other respects from the individuality differentials. 



However, if in addition to the primary blood-group differentials, we con- 

 sider other types of differentials which may be found in erythrocytes, such as 

 the accessory blood-group differentials, the Forssman and accessory hetero- 



