Antibodies and Immunity 89 



of the folding of the protein chains. Attempts have been made by 

 PauHng and Campbell to produce artificial antibodies by incubating 

 'denatured' ox globulin with an antigen. A material was obtained 

 which was capable of precipitating the antigenic substance, but it is 

 not certain that this was a real antibody similar to those produced 

 in life. 



If the antigen has to be present when the antibody is formed, we 

 have to suppose that in those cases in which immunity lasts for life, 

 the antigen also remains in the tissues as a 'pattern' all this time — 

 not withstanding the fact that we know that the lymph cells in which 

 the antibodies are formed are changed many times. 



DISORDERS ARISING FROM THE IMMUNITY MECHANISM 



The immunity mechanism is in some ways too efficient, because in 

 some rather special cases it leads to undesired reactions. For ex- 

 ample, there is the phenomenon known as 'allergy'. An individual 

 may become sensitive to a foreign protein, which may be quite com- 

 mon in his surroundings. His blood will contain antibodies to this 

 substance and, as a result, the immunity reaction occurs whenever 

 he is exposed to it. This leads to various uncomfortable and some- 

 times very troublesome effects, which are similar to those which 

 occur with infection. The temperature may rise (fever) and histamine 

 is liberated in the tissues. It is this which causes 'hay fever' and the 

 characteristic skin weals of some allergic reactions. 



It also became known, when attempts were made to perform blood 

 transfusion, that the blood of two individuals of the same species 

 frequently cannot be mixed, because agglutination occurs. This led 

 to a number of blood groups being distinguished and the recognition 

 that the blood of a donor should be of the same group as that of the 

 receiver. 



The agglutination is caused by substances analogous to antibodies 

 which are present in the serum. These antibodies, or agglutinins as 

 they are called, are naturally compatible with the corpuscles of 

 their own type of blood, but they cause agglutination with other 

 types, through a reaction which is similar to the antigen-antibody 

 reaction. 



Four main groups of blood have been recognized which are 

 labelled as follows: 



Corpuscles (antigens) O A B AB 



Plasma antibodies (agglutinins) a(3 /3 a — 



The blood group O contains antibodies to both A and B. For this 



reason it will agglutinate blood of groups A, B and also AB. On the 



