514 THE BIOLOGICAL BASIS OF INDIVIDUALITY 



pairs of this kind were tested in this manner ; in two of them antibodies were 

 readily produced, whereas in two other pairs immunization was obtained 

 with greater difficulty. In the latter cases, in testing the agglutinating power 

 of the sera for the blood corpuscles of the two partners, almost no distinction 

 was found ; correspondingly, each had very weak antigenic potency in the 

 partner. On the other hand, the partners in the first two pairs could be readily 

 differentiated from each other and, accordingly, distinct effects were obtained. 

 The agglutinating sera resulting from immunization with the erythrocytes of 

 brothers were highly specific and acted only on corpuscles of birds very similar 

 to those whose erythrocytes had been used for injection ; but towards these 

 cells they appeared to be as active as the sera prepared by injection of non- 

 related fowls ; there was again a lack of gradation. 



In chickens, individual differences were found also by Landsteiner and 

 Miller, who immunized rabbits with chicken blood. The immune agglutinins 

 in the rabbit serum could be absorbed with the red blood corpuscles from a 

 certain chicken. The remaining rabbit serum was still able to agglutinate the 

 erythrocytes from other chickens but not those from the animal used for 

 absorption; only in two pairs of chickens were the agglutinins found identical 

 in these tests. Similarly in natural ox serum multiple substances seem to exist, 

 which are able to agglutinate the red corpuscles of individual chickens. 

 Through absorption with the erythrocytes of a chicken these substances could 

 be specifically removed. Ox serum thus treated no longer agglutinated the 

 chicken corpuscles used for absorption, although it had retained the ability to 

 agglutinate the corpuscles from other chickens (Landsteiner and Levine). 

 Likewise, by injecting chimpanzees with human erythrocytes, Landsteiner 

 and Levine were able to find some differences between individual human 

 red corpuscles. However, in the case of turkey and guinea fowl blood, in- 

 dividual differences could not be established by these means. 



In the experiments of Todd, and in similar investigations of others, as 

 well as in the earlier experiments of Ehrlich and Morgenroth, the question 

 arose as to whether we have not to deal with group antigens rather than with 

 individual antigens. Thomoff, in experiments on the formation of homoio- 

 hemolysins or homoioagglutinins in horses, suggested that reactions occur 

 only if the donor of the antigen and the producer of the immune substances 

 belong to different blood groups. However, even in these experiments the 

 hemolysins or agglutinins were not primarily antibodies against the group 

 antigens of horses, but they were individual agglutinins and hemolysins, al- 

 though secondarily the group differentials may have entered as a factor in these 

 reactions. Similarly, it may be possible that also in Todd's experiments the 

 group differentials may have played a secondary role, but essentially these 

 experiments concern differentials distinguishing individuals. 



In comparing these serological tests for individuality with the analysis of 

 the individuality differential by means of transplantation, we see that in the 

 former use is made of the antigen of one type of cell only, the erythrocytes, 

 and the conclusions likewise relate merely to the differences between the 

 antigens in various kinds of red blood cells. In transplantation experiments, 



