Chapter 19 



BLOOD GROUPS 



It had long been known that blood transfusions could not be 

 made freely among all people, for sometimes the individual that 

 received the blood died almost instantly. The reason for this 

 was not clear until 1900, when Landsteiner discovered that the 

 addition of blood serum from one person sometimes caused the 

 red blood corpuscles of another to clump together. Such clump- 



a b 



Fig. 83. Agglutination of cells: (a) no agglutination; (6) cells clumped 

 together or agglutinated. 



ing, known as "agglutination" (Fig. 83), is merely one phase of 

 a general reaction known as the antigen-antibody reaction. 



An antigen-antibody reaction occurs when a substance which 

 does not normally occur in the body of a given individual is 

 injected into his blood stream. The body of the individual into 

 whom the injection is made reacts by producing substances which 

 tend to oppose or neutralize the foreign body. It is apparently 

 an attempt at protection against something which does not be- 

 long in and may therefore be harmful to the individual. The 

 protective substance formed is called the antibody, and the for- 

 eign substance that calls forth this reaction is an antigen. The 

 particular type of antibody produced depends upon the nature 

 of the antigen, and the reaction depends upon the type of anti- 

 body. 



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