292 Blood Groups 



when blood of the rhesus monkey was injected into rabbits an 

 immune serum was produced in the blood of the rabbit. When 

 this antiserum was mixed with human blood, agglutination re- 

 sulted in about 85 per cent of the cases which they tested, showing 

 that the rhesus monkey and most human beings contain this par- 

 ticular agglutinogen in their blood. They designated this ag- 

 glutinogen as Rh. Preliminary studies of the presence or absence 

 of this agglutinogen in several families indicated that it be- 

 haved as if it were the result of a certain dominant gene, which 

 can be designated R. It was further shown that in certain types 

 of matings Erythroblastosis foetalis, a familial hemolytic disease 

 of the newborn, resulted. If the mother was Rh~negative and 

 the father was Rh-positive and homozygous, the offspring would 

 be genotypically Rr, would possess the agglutinogen, and would 

 therefore be Rh-positive. 



Apparently this agglutinogen can often pass through the pla- 

 centa from the fetus and can enter the mother's blood. There 

 it will stimulate the production of the antibody or agglutinin, 

 which can also diffuse through the placenta and enter the blood 

 of the fetus. Since the blood of the fetus contains the agglu- 

 tinogen, it will be agglutinated by the introduction of the ag- 

 glutinin and the fetus may be stillborn. This reaction occurs 

 entirely independently of the blood groups of the parents and 

 fetus. It does not, however, occur in all cases in which the 

 mother is Rh-negative and the child Rh-positive. For example, 

 the first-born child is seldom affected, if at all, but apparently 

 the first Rh-positive child sensitizes the mother so that subse- 

 quent Rh-positive children are much more likely to be affected. 

 In a few cases the first-born child was affected, but in most of 

 these the mother had previously received a transfusion of Rh- 

 positive blood. Even the subsequent children, however, do not 

 die in nearly so high a frequency as is expected, for only about 

 one out of twelve pregnancies which could result in an erythro- 

 blastotic infant do so. Apparently more than one pregnancy is 

 sometimes necessary before a sufficient degree of sensitization 

 develops. 



It is quite reasonable to suppose that in some of the preg- 

 nancies which do not result in death an effect may be produced 

 which may be harmful although not fatal. Some observations 



