P^rf "Y/n Organismal Differentials and Organ Differentials 



as Antigens 



Introductory Remarks 



When pieces of organisms, organs or tissues, or when cells or parts 

 of cells are transferred to or united with other organisms or parts 

 of them, there are initiated those reactions which we have discussed 

 in the preceding chapters, and which may serve as indicators of the nature 

 of organismal and organ or tissue differentials. But in addition, the introduc- 

 tion of these tissues and cells, or of substances which are derived from them, 

 may lead to the production of new substances and mechanisms which are 

 specifically directed against the bearers of the organismal and organ differ- 

 entials. These latter kinds of reactions represent immune processes and the 

 altered state resulting in the strange organism is that of immunity ; the specific 

 substances formed in these reactions are immune substances or antibodies, 

 and the substances which initiate these immune processes and lead to the de- 

 velopment of immunity are antigens. Antigens and the corresponding anti- 

 bodies may be considered as specifically adapted substances, which may either 

 develop spontaneously or are produced experimentally. 



In this part we shall discuss the relations between organismal and organ 

 differentials and antigens. We shall also include in the discussion some sub- 

 stances which have certain characteristics in common with organismal or 

 organ differentials, but which differ from them in some respects. There are, 

 in addition, substances which are able to react in a specific way with antibodies, 

 although unaided by proteins they may not be able to initiate immune proc- 

 esses, and therefore to act as complete antigens. 



In the first chapter, we shall consider the differentials of blood groups and 

 the heterogenetic (Forssman) antigens, which while differing in certain re- 

 spects from the typical organismal and organ differentials, in some ways re- 

 semble them. 



477 



