496 THE BIOLOGICAL BASIS OF INDIVIDUALITY 



genetic antigens, it is possible that all of them combined, or even a certain 

 number of them, might suffice to distinguish individuals, but they would 

 not in all probability indicate the relationship of these individuals. But there 

 is reason for assuming that also a combination of various organ differentials 

 might differentiate between different individuals, although they would not 

 be identical with the individuality differentials. To demonstrate the identity 

 of the former with the individuality differentials, the proof would first have 

 to be given that they are qualitatively the same in all the essential tissues of 

 the same individual, and different in all other individuals ; furthermore, that 

 these sets of blood-group differentials are actually the ones which function 

 in the various individuals as individuality differentials, or that they are an 

 important constituent of the individuality and species differentials. This is very 

 improbable as far as the primary blood groups are concerned, because, as 

 we have seen, the results of homoiotransplantations are independent of the 

 distribution of these differentials; besides, the presence of similar blood- 

 group differentials in different species of animals does not affect noticeably 

 the severity of the reaction following heterotransplantation in such species. 

 The Forssman antigens, which are characteristic of very diverse species, can 

 be removed or neutralized by means of specific absorption without the species 

 differentials being affected by this procedure. However, as already stated, if 

 the number of blood-group differentials serving as agglutinogens or able to 

 give rise to the production of hemolysins is greatly increased in the individ- 

 uals belonging to a certain species, then it is possible that such sets of poten- 

 tial antigens may more and more coincide with the factors composing the in- 

 dividuality differentials. 



To recapitulate : There are at least four requirements which have to be 

 satisfied before a set of differentials can be accepted as representing the 

 individuality differentials : (a) they must make possible the distinction be- 

 tween individuals; (b) they must occur in all or almost all the tissues of an 

 individual and thus allow the distinction of the tissues of one individual from 

 the different tissues of another individual ; (c) they must indicate the relation- 

 ship of a particular individual to another individual, and (d) their inheritance 

 must not depend upon a very small number of factors which are transmitted 

 in accordance with simple Mendelian rules of alternate inheritance. The pri- 

 mary blood groups, and even the accessory blood-group differentials, as well 

 as the various heterogenetic antigens have not, so far, been shown fully to 

 satisfy these requirements. However, the possibility cannot be excluded that 

 blood-group differentials may be a constituent part of the individuality dif- 

 ferentials. It seems that a comparison of the ability of the erythrocytes to 

 absorb various chemicals, and presumably also other physiological or phar- 

 macological tests, indicate better the phylogenetic relationship of the species 

 from which the red cells to be tested are derived, than the study of the relations 

 between blood-group differentials and blood sera of various species of animals. 

 As we have stated in a preceding chapter, various tissue and organ differentials, 

 whether their significance is due to structural, biochemical or functional con- 



