H&MOLYSINS. 25 



and (2) that such a mixture of tetanus poison and 

 normal central nervous system is innocuous to an- 

 imals; because certain substances present in the 

 central nervous system combine with and thus sat- 

 isfy the affinity of the haptophore group of the 

 poison. This of course prevents the latter from 

 combining with any of the cells of the organism. 



Organs other than the central nervous system do 

 not possess this property of combining with tetanus 

 poison, just as the central nervous system is, on 

 the contrary, incapable of combining with diphthe- 

 ria poison which clinically does not show any pro- 

 nounced affinity for the central nervous system. 

 This combination, then, of central nervous system 

 and tetanus poison is a specific one in conformity 

 with the side-chain theory. Furthermore it has 

 long been known that it is possible to immunize 

 animals (and so produce antitoxins) with toxoids, 

 i.e., with poisons that possess only a haptophore 

 group. This supports the view of Ehrlich that the 

 essential feature of antitoxin formation is the com- 

 bination of the haptophore group of the poison 

 with certain definite parts the receptors of the 

 cell. Conversely, poisons or cells the affinity of 

 whose haptophore group has previously been satis- 

 fied are unable to excite the production of any 

 antitoxin excite any immunity. That is because 

 they are no longer able to combine with receptors 

 of the cells, v. Dungern, for example, showed that 

 blood-cells which had previously been saturated 



