THE VERTEBRATE BODY 



345 



are designated as O, A, B, and AB. There is no demonstrable differ- 

 ence in the quality of blood of the four types — we cannot say that any 

 one is more efficient than another. The different types of blood differ 

 in the presence or absence of certain substances known as antigens in 

 the red blood cells, and by corresponding antibodies in the blood plasma. 

 Fig. 23.12 shows the composition of the different types of blood accord- 

 ing to antigens and antibodies. If blood with the A antigen in the red 

 cells is mixed with blood that contains the A antibody, there will be a 



Type A 



a 



a 



Type B 



Type AB 



O 



© - © 



© 



a 



a 



a 



a 



a 

 a 



a a a 



® © 



AB-Anfigens 



ab-Anfibodies 



A/ 



Fig. 23.12. Diagram to illustrate the antigen-antibody constituents of the red cells and 

 the plasma of the blood. Capital letters represent antigens ; these are within the cells. 

 Small letters represent antibodies ; these are in the plasma. Whenever antigens and 

 antibodies of the same letter come together, there is agglutination of the red cells 



involved. 



clumping of the red cells containing the A antigen. If this clumping 

 occurs in the blood vessels to any great extent during a transfusion, 

 death is very likely to result. Hence, blood is carefully typed before 

 transfusion to avoid such clumping in the veins of the recipient. The 

 method of determining a person's blood type is shown in Fig. 23.13. 



There have been cases where transfusions of the proper type of 

 blood have been given and still there was a severe reaction and clump- 

 ing of the blood cells being given. Such cases can result from the 

 presence of another antigen which is known as the Rh factor. It is 



