278 STUDIES IN IMMUNITY. 



healthy animals may yet be dangerous for animals that are weak- 

 ened and so rendered more sensitive. It may be possible to ex- 

 plain in this manner the intoxication by means of diphtheria toxin 

 of animals that are actually producing active diphtheria anti- 

 toxin. Although the modification of toxin is still going on, the 

 animal may have become very sensitive to even a saturated toxin, 

 which, of course, is without effect on normal animals. The sus- 

 ceptibility of guinea-pigs immunized against the cholera vibrio to a 

 tetanus toxin-antitoxin mixture (Roux and Vaillard) is apparently 

 another example of this fact.* 



A relatively small amount of anti-alexin suffices to protect normal 

 unsensitized corpuscles from alexin, but a large amount is neces- 

 sary to protect sensitized blood cells. As Morgenroth and Sachsf 

 have already shown, more anti-alexin is necessary to protect heavily 

 sensitized corpuscles than slightly sensitized ones; in other words, 

 the toxicity of the alexin-antialexin complex depends on the 

 strength of the sensitization. 



This, leads us to a consideration of results obtained by investi- 

 gators on the injection of a toxin that is partially neutralized by 

 antitoxin. As we know, such a substance is simply attenuated 

 toxin, inoffensive for certain animals, but distinctly harmful for 

 others. Dryer and Madsen have shown that such an incom- 

 pletely saturated mixture of diphtheria toxin, which is quite in- 

 nocuous for the guinea-pig, produces slight symptoms, (edema, etc.) 

 in the rabbit. The toxicity of such a mixture might be increased 

 by varying the respective amounts of the antagonistic substances 

 and so preparing a slightly less attenuated mixture. Under such 

 conditions an animal that had only shown edema would show 

 distinct poisoning. Such results, indeed, were obtained by Dryer 

 and Madsen. 



These investigators consider that such incompletely saturated 

 mixtures contain only toxon, that is to say, a different and less active 

 substance than the true toxin. This toxon seems to us to be simply 

 our complex toxin incompletely saturated with antitoxin. Such 

 a complex has all the characteristics attributed to toxons: it is by 

 definition less toxic than free toxin and also less avid of antitoxin, 



* Such mixtures, of course, are inactive for normal guinea-pigs. 



f See Studies on Immunity, Ehrlich-Bolduan, John Wiley and Sons, p. 250. 



