14 IMMUNE SERA 



experimental proof of the second and third points, 

 the increased production of the receptors and their 

 thrusting off. For this purpose he employed a 

 tetanus poison which he had kept for about eight 

 years, and which was originally very poisonous. 

 In the course of years, however, owing to the 

 damaging action of light, of oxidation, etc., it had 

 become so weak that it was no longer toxic at all. 

 Injections of one cc. into a guinea pig produced 

 no tetanus. Nevertheless the haptophore group 

 remained intact, as could readily be proved, for 

 this non-poisonous tetanus toxin was still able to 

 bind tetanus antitoxin, i.e. thrust-off receptors. On 

 injecting rabbits with this nOn-poisonous tetanus 

 toxoid in increasing doses, and then examining the 

 blood serum of the animal he found not a trace of 

 tetanus antitoxin. This absence could have either 

 of two causes: It might be that the toxoid no 

 longer produced any physiological effect whatever 

 in the organism; or although it still caused an 

 increase in the receptors, these increased receptors 

 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, 



