IMMUNITY REACTIONS 197 



It is held by one small group of investigators that antigens are 

 lipoids or lipoid-albumin compounds. Since the part taken by lipoids 

 in many immunity reactions 'is not definitely settled, it is impossible 

 as yet to determine the general correctness of this view. At any 

 rate it has not as yet been possible to immunize with the lipoids 

 chemically known. 



Since our knowledge concerning the chemical composition of 

 normal proteins is still meager, what we know about the proteins of 

 immune bodies cannot be more ample. According to KIRSCHBAUM 

 dysentery toxin is acid. By ultrafiltration, he prepared water insolu- 

 ble acid dysentery-toxin which was nearly atoxic, though the salt 

 obtained by dissolving the acid in an alkaline carbonate possessed 

 the poisonous properties of the toxin. The experiments of FR. 

 OBERMAYER and E. P. PICK* indicate that the aromatic nucleus in 

 the antigen is of great importance for the development and character 

 of the antibodies. 



Antibodies are universally regarded as albuminous. 



Before we discuss details } let us indicate a great misunderstanding 

 which at the time gave rise to heated discussions and clouded the 

 issues. The quantitative relations in which the substance in ques- 

 tion enters into reaction (toxins with their antitoxins, bacteria with 

 their agglutinins, etc.) have great similarity to adsorption curves 

 (W. BILTZ) and to the neutralization curves of certain weak acids 

 and bases (Sv. ARRHENIUS). These investigators laid great stress 

 on this fact and believed that they had thus discovered the nature 

 and the course of the immunity reactions in question. P. EHRLICH 

 raised the weighty objection, that the reaction is specific, and that 

 the poisons are very complex: diphtheria toxin is detoxicated only 

 by diphtheria antitoxin; typhoid bacilli are precipitated only by 

 typhoid agglutinin. There is no doubt that these specific proc- 

 esses cannot be explained by what we call colloid-chemical reactions 

 (see H. BECHHOLD* 3 ). We must conceive of the process as occurring 

 in two stages, and we must emphasize that this sharp distinction 

 does not obtain in every case. 



First Stage: The two colloids, toxin and antitoxin, bacterium and 

 agglutinin, unite in accordance with the laws governing other colloids, 

 e.g., fiber and dye, and the specific substances react on one another 

 and it is still an open question whether we must represent these 

 reactions as chemical or catalytic. 



Second Stage. The colloidal product of the reaction shows physical 

 properties which distinguishes it from the reacting substances, e.g., 

 it precipitates. 



We cannot enter here into the question of specific combination. 



