THE VERTEBRATE BODY 



347 



named from the Rhesus monkey in whose blood it was first demon- 

 strated. All Rhesus monkeys and about 85 per cent of the Caucasian 

 race in the United States carry this antigen. We say that these are 

 Rh positive. The 15 per cent who do not carry the antigen are Rh 

 negative. Normally, the blood plasma of an Rh negative person will 



^eS 



Negative mother 



Negative child 



Baby normal 



Same mother 



Positive child 



Baby normal 



Mother sensitized 



Same mother 

 Second positive child 

 Baby born with 

 erythroblastosis 



Fig. 23.14. How the Rh factor may cause erythroblastosis. When an Rh negative 

 woman bears a negative child there is no trouble. Neither is there any trouble with 

 her first positive child, but the Rh factor from this child may cause her to become 

 sensitized and her body then contains Rh antibodies. Future positive babies will de- 

 velop erythroblastosis due to the reaction of these antibodies with the Rh factor in 



the embryos. 



not carry any antibodies for the Rh antigen, but such antibodies may 

 be developed if a person contacts the antigen. This is somewhat like 

 the development of antibodies against the antigens which are present 

 in disease germs after the body is invaded with these germs. Such 

 antibodies help us fight these germs in future contacts with them. 

 When a negative person receives a transfusion from a positive person, 

 there will be no reaction if this is the first such transfusion and the 



