Ill 



THE FACTS OF IMMUNITY 



A theoretical approach to any field of science is something of 

 a luxury. The practical affairs of the world always seem to run 

 along smoothly, or at least normally, without recourse to the 

 theoretical generalizations that are currently worrying the 

 minds of scientists. In that sense they are unnecessary, but 

 we do not have to look far to find something very practical 

 going on around us which is completely dependent on an 

 understanding of what twenty, fifty, or one hundred years 

 ago was a tentative and controversial generalization. 



Any discussion of a many-angled field like that of im- 

 munology will reflect the major interest of the person 

 responsible for it. In my own case the approach has tended 

 to oscillate between an interest in the specific patterns of 

 macromolecules and a special concern for the epidemio- 

 logical implications of immunity. It has always been biased 

 toward the biological, rather than the chemical side. The 

 facts of immunity that I want to summarize are those which 

 seem most relevant to any attempt to look at the immune 

 responses as a part of the general biological picture. 

 They can be listed as follows: 

 (i) The physical nature of the populations of reactive 



globulin molecules in a typical antiserum, 

 (ii) The differences, quantitative and qualitative, between 



primary and secondary response. 

 (iii) The lack of immunological reactivity to body com- 

 ponents and the related phenomena of tolerance. 

 (iv) The qualitative types of immune response. 

 (v) Congenital agammaglobulinaemia. 

 (vi) The part played by mesenchymal cells, particularly 

 those of the lymphoid series, in immune reactions. 



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