482 THE BIOLOGICAL BASIS OF INDIVIDUALITY 



organs, such as liver and kidney, may have certain receptors in common; in 

 this respect the blood-group differentials resemble the organismal differen- 

 tials. 



From what has been stated, it follows that by means of the four primary 

 blood groups it is not possible, as a rule, to differentiate one individual from 

 another, nor to indicate the degree of relationship between individuals. The 

 behavior of transplanted tissues, on the other hand, does show not only the 

 distinctiveness, but also the relationship of individuals in an approximately 

 quantitative manner. All degrees of relationship are revealed by transplanta- 

 tion. This difference between the factors determining the results of transplan- 

 tation and the differentials of blood groups among individuals belonging to 

 the same, as well as to different species, is also emphasized by the lack of 

 parallelism between the results of transplantation and blood-grouping. We 

 have seen previously that the results of skin transplantation among human 

 beings are not noticeably influenced by the blood groups to which these 

 individuals belong. In animals transplantation reveals individual differences, 

 although blood-group differences may be lacking here altogether. Furthermore, 

 the presence of similar group differentials in different species of animals does 

 not affect noticeably the severity of the reaction following heterotransplanta- 

 tion in these species. 



What applies to the relations between the organismal differentials, as ana- 

 lysed by means of transplantation, and the human blood groups applies also, 

 and to a still greater extent, to the relations between the heterogenetic dif- 

 ferentials of Forssman and the organismal differentials. The Forssman differ- 

 entials are in some respects the opposites of the organismal differentials ; the 

 latter correspond to and express the systematic relationship of organisms, 

 whereas the Forssman differentials disregard these relationships; as stated 

 they are factors held in common by the most varied and often distant kinds of 

 organisms, without regard to systematic relationship. We may, perhaps, com- 

 pare them in part with certain pigments which are present in the epidermis of 

 the most varied species, without reference to their systematic position. 



In many species of animals there occur in the blood corpuscles, species- 

 specific agglutinogens, and in the blood serum, species-specific agglutinins, 

 which latter cause agglutination of the blood corpuscles of foreign species, 

 without reference to the blood-group to which they may belong. Inasmuch as 

 these agglutinins are directed against heterogenous species, they are called 

 heteroagglutinins ; they are not, at least in some cases, experimentally or 

 accidentally produced immune substances, but are preformed substances. 

 At present it is not possible to establish a direct relationship between pre- 

 formed heteroagglutinins and the organismal differentials, except that in 

 some cases, when two species are relatively nearly related, heteroagglutinins 

 seem to be lacking, as in the case of rat and mouse, or of buffalo and cattle ; 

 however, human serum may contain heteroagglutinins for the erythrocytes 

 of nearly related anthropoid apes. In addition, there may occur in the serum 

 of these species, hemolysins which are similar. Distinct from these preformed 

 heteroagglutinins in the sera of various animal species are immune agglutinins 



