344 Chapter XII 



[361] unstable. The methods adopted by Roux and Yersin in their study 

 of diphtheria toxin enabled other investigators to discover the analo- 

 gous toxins of several other bacteria. Knud Faber^ and Brieger and 

 FrankeF soon succeeded in separating the toxin from the tetanus 

 bacillus, a toxin capable of producing in animals tetanic contractions 

 as typical as those obtained with cultures of the tetanus bacillus. 



These investigations inaugurated a new era in microbiology and 

 enabled us to attack the problem of acquired immunity against 

 bacterial toxins scientifically. Within a few months of the declaration 

 made by Bouchard at the Berlin Congress, there appeared, almost 

 simultaneously, the earliest publications on the possibility of vaccinat- 

 ing laboratory animals against the toxins of diphtheria and tetanus 

 by artificial methods. Immediately after the discovery of these 

 poisons, the attempt was made to immunise various species of animals 

 against them, but here very great difficulties were met with; the 

 animals, after receiving increasing doses of toxin, became thin 

 and ultimately died. It occurred to FrankeP that the toxic 

 action of the diphtheria poison might be weakened by subjecting 

 it to a temperature of 60° C. Independently, von Behring and 

 Kitasato* used chemical substances, especially iodine trichloride, to 

 attenuate the action of the tetanus and diphtheria toxins. The 

 animals which resisted these modified poisons were found to be 

 capable of tolerating gradually increasing doses of unaltered and 

 very active toxins. By the use of these methods it was found 

 possible to obtain a definite and lasting immunity against these 

 microbial products. 



The discovery of the possibility of vaccinating against bacterial 

 toxins was soon followed by the demonstration of the antitoxic power 

 of the blood of animals that had acquired such artificial immunity 

 against these poisons. Everyone knows of and appreciates von Behring 

 and Kitasato's great discovery. It opened up a new and fruitful field 

 of research from most diverse points of view. Ehrlich^ was able to 



[362] apply it to the vaccination of animals against the vegetable poisons 

 ricin, abrin and robin, and thus to establish rigorous methods of im- 

 munisation and to obtain very important results concerning immunity 

 against toxins in general. He also succeeded in demonstrating that 



^ Berl. klin. Wchnschr., 1890, S. 717. 



2 Berl. klin. TVchnschr., 1890, No. 11. 



3 Berl. klin. Wchnschr.^ 1890, No. 49. 



* DeutscJie med. Wchnschr., Leipzig, 1890, SS. 1145, 1245, 

 ^ Deutsche med. TVchnschr,, Leipzig, 1891, SS. 976, 1218. 



