ANTITOXIN. 7! 



If an animal, e.g., a goat is injected with a sublethal dose of 

 Active Immu- diphtheria toxin and after the lapse of a certain period of time 

 nization it is reinjected with a lethal dose, the animal remains alive. 

 against In fact it may receive numerous fatal doses, and still survive, 

 a Toxin. ^his experiment is the simplest in active immunization 

 against a toxin. The explanation of the action which has 

 taken place, an examination of the blood serum of the immunized animal 

 will disclose very readily. If this serum is mixed with a fatal dose of toxin 

 and the mixture inoculated into a normal guinea-pig, the latter remains alive 

 and perfectly active. The serum of the immunized animal 

 Antitoxin, therefore contains a protective agent which is directed against 

 the toxin and destroys its activity; hence the name antitoxin. 

 But the antitoxin is specific, i.e., diphtheria antitoxin neutralizes only diph- 

 theria toxin and not tetanus. The recognition of these facts and those 

 heretofore mentioned, and the recommendation of the therapeutic use of 

 diphtheria serum belongs entirely to v. Behring and righteously may he be 

 called the father of serum therapy. 



Although theoretically, the serum of any animal immunized with diphtheria toxin can 

 serve as a curative serum for diphtheria, practical experience has taught that it is best 

 to employ horses for this purpose. For laboratory experiments goats should be the ani- 

 mals of choice. It is advisable to use the above animals for the reason that larger quanti- 

 ties of serum are obtained and furthermore because it has been found impossible to immu- 

 nize guinea-pigs with previously unchanged diphtheria toxin even if the initial dosage used 

 is the smallest subdivision of the minimal lethal dose. Behring and Kitashima showed that 

 after repeated injections of very minute doses they were able to kill guinea-pigs even 

 with 1/400 of the dosis letalis minima. This is but another example of an effect just 

 opposite to that of immunity and known as hyper -susceptibility or hypersensitiveness, which 

 has already been described in the chapter on tuberculin therapy. If, however, it is de- 

 sired to immunize guinea-pigs, a modified form of the diphtheria toxin must be employed 

 for the first injections. Several modifications are feasible. Behring and Kitasato added 

 iodin trichlorid to the toxin while Roux and Martin, LugoPs solution; C. Frankel heated 

 it to 60, and Behring advocated the so-called " simultaneous method" (of special aid in 

 tetanus toxin), where mixtures of toxin and antitoxin are injected and gradually the 

 quotient of the latter is diminished until finally it is entirely omitted. If the animals have 

 borne the first inoculations of the modified toxin without any ill effects, one may then 

 devote himself to the use of the unmodified toxin. 



In contrast to small animals, horses can be immunized with unmodified diphtheria 

 toxin right from the start. Nevertheless great care must here also be exercised. Certain 

 it is, that less risk is run in the employment, with even the larger animals, of a modified 

 toxin. For the production of a good diphtheria serum, healthy horses about five to six 

 years old are used and into them gradually increasing amounts of diphtheria toxin are 

 injected subcutaneously or even intravenously; thus agreeing with Ehrlich's findings 

 to the effect that the antitoxin content of a serum can be raised by successively increasing 

 the amount of toxin injected. As far as the efficiency of the serum produced is concerned, 

 it is entirely dependent upon the animal. Horses vary greatly in their individual pre- 

 disposition towards the making of an effective serum; some animals even completely 



