24 IMMUNE SERA 



remained in the organs (sessile) and were not 

 thrust off into the blood. In order to decide this 

 question Wassermann first determined the exact 

 quantity of fresh tetanus toxin which constituted a 

 fatal dose for guinea pigs. He reasoned that if 

 he injected first the toxoid, and shortly after, say 

 in one or two hours, the fresh toxin, he should in 

 such an animal have to increase the fatal dose, 

 i.e. more tetanus toxin should be required to kill 

 this animal than a normal one, because owing to 

 the previous toxoid injection part of the cells sus- 

 ceptible to tetanus toxin would already have been 

 occupied. Provided Ehrlich's theory were correct, 

 so that this binding of the toxoid really occurred, 

 the conditions should be entirely different when, 

 instead of injecting the toxin shortly after the 

 toxoid, he waited somewhat longer, one to three 

 days, and then injected the fresh tetanus toxin. 

 In that case Weigert's law should come into play 

 and the receptors have commenced to increase 

 in number, i.e. the organ should now possess more 

 sensitive groups than before. This would manifest 

 itself in such fashion that in contrast to the first 

 experiment the fatal dose of fresh tetanus toxin 

 could now be decreased ; in other words a small dose 

 would now tetanize the animal in a shorter time. 



As a matter of fact Wassermann 's experiments 

 yielded exactly the results deduced theoretically. 

 He injected a guinea pig with some of the non- 



