SIDE-CHAIN THEORY 187 



still combined with antitoxin that is, toxoids with 

 haptophore groups were still present they found that 

 on injecting it into animals no antitoxin was formed as a 

 result of the injection. They then performed experiments 

 based on the following line of reasoning : If the old non- 

 poisonous tetanus toxin containing these toxoids be first 

 injected into an animal, and after a short interval some 

 fresh, actively poisonous tetanus toxin, more of the active 

 toxin ought to be required to kill this animal than a 

 normal one, because, owing to the previous toxoid injec- 

 t'on, some of the cell receptors susceptible to tetanus toxin 

 are already occupied. Provided Ehrlich's theory be 

 correct, and that this binding of the toxoid really occurs, 

 the conditions should be entirely different, when, instead 

 of injecting the toxin shortly after the toxoid, a longer 

 time elapsed one to three days before the injection of 

 the active tetanus toxin. For in that case Weigert's law 

 should come into play and the receptors should have 

 increased in number i.e. the animal would now possess 

 more sensitive groups than before. This should be mani- 

 fest by the fact that, in contrast to the first experiment, 

 the fatal dose of active tetanus toxin ought now to be 

 smaller than previously ; in other words, a smaller dose 

 should now tetanise the animal in a shorter time. The 

 experiments yielded results which were exactly in 

 accordance with these theoretical considerations. A 

 guinea-pig was injected with some of the non -poisonous 

 toxoid, and then, one hour later, with the active tetanus 

 toxin. It was found that much more toxin was required 

 to kill this animal than a normal guinea-pig of equal size. 

 If, on the contrary, an interval of one to three days were 

 allowed to elapse, it was then found that a dose of tetanus 

 toxin which would not even tetanise a normal guinea-pig 

 was sufficient to kill the treated one. 



The fact that no antitoxin was formed i.e. no receptors 



