1 88 MANUAL OF BACTERIOLOGY. 



Another remarkable property is that toxin that has stood for a long time 

 loses greatly in poisonous properties, but not in its power of combining with 

 antitoxin. Furthermore, this old toxin will produce antitoxin if injected into 

 horses or other susceptible animals. 



In order to explain these extraordinary reactions several theories have been 

 advanced, and in this connection certain peculiar reactions obtained with 

 lysins, agglutinins, and precipitins, which have helped to give an insight, have 

 also been explained on similar theoretical grounds. These theories will now 

 be discussed. 



EhrUch regards the beef-broth from a diphtheria or tetanus culture as a 

 solution of several different but related bodies, and he makes so-called "spectra" 

 to explain this idea. He thinks that primarily the substances are toxin and 

 toxon (Fig. Sr), each having affinity for antitoxin; but the affinity of toxon 

 for antitoxin is weaker than the affinity of toxin for the antitoxin. And, further- 

 more, toxon — no matter in what dose — does not kill guinea-pigs quickly if at 

 all, but causes a paralysis of the animal after some weeks of incubation, while 



Fig. 51. — "Spectrum" or Theoretically Fresh, Crude Toxin. 

 Such a combination probably does not occur. 



toxin, on the other hand, in just the proper amount kills a guinea-pig weighing 

 250 grams in two days. This is the standard minimum fatal dose, or i d. 1. 

 (dosis letalis). 



Now, if enough antitoxin is added to the poisonous beef-broth it will neu- 

 tralize both the toxin and the toxon, but if not enough is added for this, the 

 toxin is first neutralized and the toxon still produces paralysis of the guinea-pig. 



But on standing, both toxin and toxon quickly become changed; a part of 

 the toxin is converted into a body called toxoid and a part of the toxon into 

 toxonoid, and, while retaining their affinity for antitoxin, these are both weak- 

 ened in pathogenic power as compared with the original toxin; toxoid, in fact, 

 is devoid of toxic properties. Toxoid, then, is toxin deprived of its toxophore, 

 but it retains the haptophore group. Still further, the resulting toxoid and 

 the toxon have each three different degrees of affinity for antitoxin. 



A part of the toxoid has less affinity than the toxin; n part equal; » part 

 more. These are designated epitoxoids, syntox'oids and proto.xoids, respec- 

 tively (Figs. 32 and 53), and toxons are in like manner designated epitoxons, 



