INDIVIDUALITY DIFFERENTIALS AND BLOOD GROUPS 151 



tissues or organs in the same organism have in common a chemical charac- 

 teristic, which differs from those present in every other organism. These 

 differences are genetic in origin and are therefore proportional to the genetic 

 relationship between different individuals, but they are not identical with the 

 genes. Such individuality differentials must be distinguished from the tissue 

 differentials, which are the same in the corresponding tissues in different in- 

 dividuals, but which differ in different tissues of the same individual. Also, 

 the red blood corpuscles possess these individuality differentials. At first, by 

 means of the study of the fate of transplanted blood clots, and especially of 

 the cellular reactions of the host against them, merely the presence of heterog- 

 enous, but not of homoiogenous, individuality differentials could be definitely 

 established, but subsequently, by the use of the white blood cell reaction, 

 Blumenthal could demonstrate also the presence of homoiogenous differentials 

 in blood clots, and correspondingly, in the erythrocytes included in these 

 clots, or at least reactions were found similar to those elicited by homoiog- 

 enous differentials present in the various tissues. 



Following the experiments of Ehrlich and Morgenroth, who succeeded in 

 producing hemolysins for homoiogenous erythrocytes in goats, Todd extended 

 these investigations and obtained similar hemolysins for homoiogenous red 

 corpuscles in cattle and sheep. In 1911, he found differences between red 

 blood corpuscles of individuals in certain species by using the differential 

 absorption method. These antigenic differences between the erythrocytes of 

 individual animals could be readily demonstrated, except in cases where there 

 was a close relationship between two individuals. In 1930 and 1931, this in- 

 vestigator prepared polyvalent homoio-(iso) agglutinating immune sera 

 against fowl erythrocytes, and again, by using the differential absorption 

 method, he found that the red blood cells of each individual examined differed 

 from those of every other individual. Also, members of the same family 

 differed from one another in the agglutinogens of their blood corpuscles, the 

 degree of difference varying very much in individual cases. The investiga- 

 tions of Todd on antigens present in the erythrocytes of cattle were recently 

 confirmed and extended by Ferguson, Stormont and Irwin, who, by repeated 

 injections of one individual with the erythrocytes of another individual of 

 this species, prepared homoiogenous hemolytic sera, or by injecting a rabbit 

 with such erythrocytes, they prepared heterogenous hemolytic sera ; they 

 furthermore analyzed the antigens present in the erythrocytes in an indi- 

 vidual animal by means of these two kinds of sera. These tests were refined 

 by absorption of the antibodies from the immune sera by the erythrocytes of 

 individual animals. Thus, these investigators found thirty different antigens 

 giving origin to immune hemolysins. Each individual differed from all other 

 individuals tested in the combination of the antigens present in its red cor- 

 puscles. There were indications that other antigens might be added to this 

 number. There were moreover, strong indications that each separate antigenic 

 substance was determined by a single dominant gene and that correspondingly 

 many multiple genes determined the set of antigens in a certain individual. It 

 is very likely that by using for immunization other species in addition to the 



