viii PREFACE 



products react, as proteins and ferments, are to be here 

 considered with respect to their chemical properties. And 

 for the purpose of a clarification of ideas, other substances 

 that behave in an analogous manner will be given a con- 

 sideration in the discussion. 



It is evident that the objection recently raised by Ehrlich 

 and Sachs to this manner of investigation, namely, that 

 it does not enter upon the mode by which the living 

 body produces these so-called antibodies, is quite true. 

 An investigation of the chemical relations of toxin and 

 antitoxin need not carry with it an elucidation of the 

 synthesis of the antitoxin. But I fancy that there are 

 many who are so deeply interested in the chemical be- 

 haviour of these substances that they will find an investi- 

 gation of this question well worthy of study. And for 

 myself, furthermore, I believe that the physiological side 

 of the problem, alluded to by Ehrlich, will not find a satis- 

 factory solution until the more simple chemical aspect is 

 elucidated. 



The chief purpose of theoretical considerations is to 

 afford clear and concise ideas of the observed facts. They 

 thereby stimulate scientific research to a high degree. I 

 venture to hope that the reader of the following pages will 

 find that the theoretical views advanced by myself in this 

 branch of science have fulfilled their role in a most satis- 

 factory manner during the few years that they have been 

 employed. I am glad to say that during these few years 

 a large experimental material has been produced, which 

 shows that the chief lines pointed out by theory are closely 

 congruent with the facts ; and this material has been pro- 

 duced almost exclusively in order to verify the said theo- 

 retical considerations. These have, therefore, already been 

 of great scientific use, and yet this is only a small part of 



