IMMUNITY 229 



We have already mentioned the old opinions of Buchner and 

 Roux. Buchner considered that the antitoxin was derived 

 from the toxin, and Metchnikoff advanced the opinion that 

 certain body-cells might produce this transformation. But, 

 it has been protested, how could a horse react to a single unit 

 of toxin by producing 100,000 units of antitoxin ? The toxin 

 may, however, be seized by certain organs which retain it for 

 a long period and transform it slowly. The toxin may induce 

 in the cells which produce antitoxin the very stimulus which 

 Ehrlich was among the first to appeal to. The experiment of 

 Roux and Vaillard on rabbits immunized against tetanus 

 would thus be explained : after repeated bleedings the 

 antitoxin power of the blood rapidly regained its former 

 titre. But why should the serum of healthy animals sometimes 

 have a certain antitoxic power? Because without having 

 actually suffered from diphtheria or tetanus they may have 

 harboured diphtheria or tetanus bacilli in their bodies : in 

 the intestine of the horse for example the tetanus bacillus 

 abounds. 



Whether or not the toxin is transformed into antitoxin, it is 

 certain that the antitoxin is a product of the body : no other 

 way of producing it is known. Ehrlich formerly thought that 

 the cells sensitive to the toxin were its chief producers ; but 

 if this were true, antitoxin ought to be present in these cells 

 and be capable of neutralizing the toxin. Wassermann and 

 Takaki's experiment seemed to prove this : the brain tissue of 

 mammals ground up with tetanus toxin, neutralizes it, furnish- 

 ing a mixture which no longer gives tetanus to animals. But 

 Wassermann's experiment has in reality a quite different 

 signification. The brain does not act as an antitoxin, for, 

 if injected into a guinea-pig along with a dose of toxin, but at 

 separate points in the body, it has no protective action what- 

 ever, and does not act in the least like a dose of antitoxin. 

 Further, if the so-called neutral mixture is injected into the 

 thigh of a guinea-pig, the animal becomes tetanic, whereas it 

 remains protected if the injection is made into the peritoneum. 

 The neutralizing property is in reality a property peculiar to 



