488 THE BIOLOGICAL BASIS OF INDIVIDUALITY 



blood corpuscles and sera. Employing these methods Hektoen obtained nega- 

 tive results, but von Dungern and Hirszfeld reported some which were posi- 

 tive, although the reactions in these animals were weaker and more irregular 

 than in man. The conclusions became more definite when not only blood 

 corpuscles and sera from individuals belonging to a certain species of animals 

 were compared, but when, in addition, the interactions between sera and 

 blood corpuscles of these animals with the well defined human agglutinogens 

 and agglutinins were studied ; and furthermore, when use was made of im- 

 mune sera, obtained in rabbits by injection of human or animal blood cor- 

 puscles, and when comparative absorptions of the antibodies, present in the 

 immune sera, by human as well as by animal erythrocytes or their alcohol 

 extracts were also considered. By these means the identity of certain group 

 agglutinogens in human erythrocytes and in the erythrocytes of more remote 

 animal species has apparently been demonstrated, as well as the identity of 

 certain agglutinins in animal and human sera, while other blood-group dif- 

 ferentials and agglutinins have been found to be limited to man or to various 

 species of animals. 



However, in some instances it has been possible to establish the presence 

 of blood groups in animal species by the same methods which have been used 

 for this purpose in man. Thus Hirszfeld and Przesmycki, and also Schermer 

 and Hofferber, have shown that in the horse four groups exist, which are 

 analogous to those in man, namely, O-alpha, beta, A-beta, B-alpha, and AB-oo. 

 The similarity between the blood groups of man and horse goes still further. 

 Thus in both of these species, analogous subgroups A x and A 2 , and two 

 agglutinins, alpha x and alpha 2 , can be recognized ; in both instances the differ- 

 ences between these subgroups are presumably of a quantitative rather than 

 a qualitative character. Furthermore, in addition to the primary four blood 

 groups, four additional blood groups, X, Y, Z and N, comparable to the 

 additional blood groups M, N, P and H in man, are demonstrable in horses 

 (Schermer and Kaempffer). 



Similarly, by means of injections of rabbits with the erythrocytes from other 

 rabbits, Fischer and Klinckhard prepared immune sera which agglutinated 

 blood corpuscles from certain groups of rabbits. They believed they were 

 able in this way to establish the existence of two agglutinogens and two ag- 

 glutinins, and they divided therefore these animals into four groups, corre- 

 sponding to the four groups found in man, although neither agglutinogens nor 

 agglutinins were identical with those of man. However, Levine and Land- 

 steiner, by immunizing rabbits with the hemolyzed blood corpuscles of other 

 rabbits, obtained a larger number of agglutinins, and they assume therefore 

 the occurrence of individual blood differences in rabbits similar to those which 

 have been established in goats, cattle and chickens, and which we shall discuss 

 in a subsequent chapter. But there occurs in certain rabbits a condition which 

 differs from the usual findings in man and in other animals. There may be 

 observed in these particular animals a peculiar distribution of the A differen- 

 tial ; it is lacking in their erythrocytes but is present in their organs, and some 



