494 THE BIOLOGICAL BASIS OF INDIVIDUALITY 



agglutinogens and it was merely hidden by its union with these agglutinogens, 

 then it should be possible by means of an intense immunization to produce 

 enough anti-A agglutinin to overbalance the slight amount of A receptor pres- 

 ent in the blood plasma. Or if it is assumed that the red blood corpuscles 

 themselves can bind and inactivate this immune agglutinin, then an ag- 

 glutination of the erythrocytes should take place in the immunized animal. 

 Such an effect however seems not to have been observed. Similarly, as men- 

 tioned already, antibodies for the Forssman antigen cannot be produced in 

 animals which belong to a Forssman positive species, although in this case 

 erythrocytes do not need to contain the heterophile differential. 



Taking these various considerations together, we think it much more 

 probable that in the case of the blood groups we have to deal with the same 

 phenomenon as in the case of the organismal differentials, namely, that in the 

 same organism mutually incompatible constituents do not develop, and that 

 the normal constituents within the body, especially if they are present also 

 in the bodyfluids, cannot serve as antigens, and that this is due to the fact 

 that in the same organism the analogous proteins and, in particular, certain 

 globulins possess some essential similarity in chemical structure irrespective 

 of their situation in the individual. The production of antibodies can take 

 place, as a rule, only when these differentials show a definite divergence in 

 chemical constitution in host and donor. 



Organismal differentials, primary blood-group differentials, the more re- 

 cently discovered accessory differentials occurring in human and also in 

 certain animal erythrocytes, as well as the heterophile Forssman differentials, 

 all have this characteristic in common, that they are genetically fixed con- 

 stituents of the various organisms and do not owe their origin to environ- 

 mental factors. As to the mode of inheritance, there are differences between 

 the organismal, and in particular, the individuality differentials and the pri- 

 mary as well as the accessory blood-group differentials. The individuality dif- 

 ferentials depend, as we have discussed previously, upon the presence of 

 multiple factors, the number of which must be considerable. On the other 

 hand, the inheritance of the primary blood-group differentials seems to de- 

 pend upon three allelomorph factors, according to the analysis of human 

 inheritance by Bernstein, whose interpretation has now been almost generally 

 accepted. The inheritance of the primary blood-group differentials follows 

 therefore a much simpler scheme than the inheritance of the individuality 

 differentials. Among the latter many fine gradations exist, while among the 

 former there is only a small number of variables. According to Landsteiner, 

 Schiff, and other investigators, the inheritance of the accessory factors M and 

 N is contingent on the presence of an allelomorph pair of genes. The possible 

 combinations of these two genes are M M, N N and M N. The factor P also 

 seems to be fixed by heredity. It has been observed that when neither of the 

 parents contains P, none of the children contain it. The factor H is believed 

 to be represented by a single dominant gene. We may then conclude that 

 the mode of inheritance of the primary blood-group differentials differs not 



