158 A MANUAL OF BACTERIOLOGY 



toxicity, but which still combined with antitoxin that 

 is, toxoids with haptophore groups still present they 

 found that on injecting it into animals no antitoxin 

 was formed as a result of the injection. They then per- 

 formed some experiments based on the following line of 

 reasoning : If the old non-poisonous tetanus toxin con- 

 taining 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 injection, part of the cell receptors 

 susceptible to tetanus toxin are already occupied. Pro- 

 vided Ehrlich's theory be correct, so 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 organism would now possess more sensitive groups 

 than before. This should be manifest 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 this one. 

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



