416 THE NEW INDIVIDUAL Part IV 



compositions of blood are diflercnt. Only a little blood from an animal of one 

 species is harmful or fatal to an animal of another species if injected into the 

 vessels of the latter. The blood of different persons also differs. It is well 

 known that human blood is affected by the chemical composition of blood in 

 certain persons and not in others. This is the basis of blood groups, the in- 

 herited chemical compositions of blood discussed in Chapter 7. It is also the 

 basis of Rh, an hereditary characteristic in the chemical content of the blood. 

 In dealing with this the meaning of the terms antigen and antibody should be 

 clear. 



An antigen is any substance, often one injected into the body, that stimu- 

 lates the formation of the chemical substances called antibodies. The toxin of 

 an infection is an antigen which stimulates the formation of antibodies (anti- 

 toxins) that turn about and work against it. 



Rh Protein. Up to a comparatively few years ago, the cause of deaths of 

 many infants before birth or soon afterward was a mystery. However, in 1940 

 a new type of human blood group was discovered which proved to be the 

 cause. It was named the Rhesus or Rh type after the Rhesus monkeys whose 

 blood was used in making tests that led to the discovery. About 85% of the 

 human population are Rh-positive, that is their red blood cells contain the 

 characteristic Rh-protein, an antigen, which reacts to the tests. The Rh pro- 

 tein is inherited through dominant genes, Rhrh or RhRh. The remaining 15% 

 of the population inherit recessive genes, rhrh. Their red cells lack the Rh 

 substances and they are termed Rh-negative. 



The connection between the Rh blood and the harm to children arises only 

 when the mother is Rh-negative and the unborn child is Rh-positive (Rhrh), 

 through inheritance from its father. The Rh-proteins (antigens) pass from the 

 blood of the child to its mother's blood where they stimulate the production 

 of "anti-Rh" substances, that is, antibodies against themselves. Eventually 

 some of this anti-Rh passes into the child's blood (Fig. 20.24). There it may 

 cause such agglutination (sticking together) of the red cells that the child can- 

 not survive. This does not usually happen with a first baby because not enough 

 anti-Rh is then produced, but more accumulates with the second or third child 

 usually with grave results. 



The "anti-Rh" substance occurs in the blood and tissue fluid and can pene- 

 trate the membranes that separate the blood of mother and child. But the Rh- 

 protein is in the child's red blood cells which would not be expected to get 

 through the membrane. How this happens remains to be discovered. 



Testing for Rh blood is a common procedure. When a Red Cross blood 

 donor is typed, the identification card includes an Rh+ or Rh— . Babies that 

 are born alive but with damaged blood may be saved by transfusions of Rh— 

 blood. The damaged blood with its dangerous anti-Rh is literally washed out 

 of the blood vessels by the donor's blood. 



