CHEMICAL CONSTITUTION AND PHARMACOLOGICAL ACTION 433 



stracted from the cells with water; it must first be split off by means 

 of acids in order to set it free. Such a chemical union, however, just 

 as every synthesis, presupposes the presence of two combining groups 

 of maximal chemical affinity which are fitted to one another. Those 

 groups in the cell which anchor foodstuffs I term "side-chains" or 

 "receptors;" the combining group of the food molecule the "hap- 

 tophore group.' Hence I assume that the living protoplasm pos- 

 sesses a large number of such "side-chians" and that these in virtue 

 of their chemical constitution are able to anchor the greatest variety 

 of foodstuffs. In this way the cell's metabolism is made possible. 



This view of the constitution of the protoplasmic molecule has 

 made it possible to get a much clearer insight into the action of the 

 toxins and into the hitherto mysterious phenomenon, the formation 

 of antibodies. I assume that the toxins, just like the food mole- 

 cules, possess a particular haptophore group, which, by fitting into 

 the receptor of the cell, gives rise to the poisonous action. Putting 

 this receptor out of action causes a formation of new receptors to 

 replace it, and these are finally thrust off into the blood. The re- 

 ceptors thus present in the blood constitute the antitoxin. This 

 theory, known as the "side-chain theory/' has proven its worth in 

 the hands of numerous investigators, for by its means the manifold 

 reactions of immunity are all led back to the simplest processes of 

 cellular life. 1 



Hence I assume the presence of a haptophore group only in such 

 combinations which, like the, foodstuffs, enter into the substance of the 

 protoplasm, or which, like the large number of poisonous and non-poison- 

 ous metabolic products of living cells, effect a union similar to that of the 

 foodstuffs. 



The marked difference between the two classes of substances 

 becomes plainly evident by the fact that only those substances possess- 

 ing haptophore groups are able to excite the production of antibodies 

 through immunization. And despite the most painstaking efforts 

 neither other investigators nor I have ever succeeded in producing 

 any appreciable production of antibody with alkaloids, glucosides, 

 or drugs of well-known chemical constitution. 



' I content myself here with these brief remarks and refer the reader to 

 my more recent detailed articles: 1. On Immunity, etc., Croonian Lecture, 

 Proceedings of the Royal Soc., Vol. 66, 1900. 2. Schlussbetrachtungen zur 

 Ana?mie, in Nothnagel's Handbuch, Vol. VIII, 1901. pages 555 et seq. 3 Die 

 Schiitzstoffe des Blutes, page 364 of this volume. 



