The ''Lateral-chain Theory" of Immunity 131 



The most suggestive and fascinating theory of immunity 

 is that of Ehrlich, and is known as the " Seitenkettentheorie" 

 or the "Lateral-Chain Theory."* 



He began his studies by an investigation into the nature of 

 toxins and their mode of action. The discovery that there 

 was no constant relation between the intoxicating and 

 antitoxin combining powers of diphtheria toxic bouillon led 

 him to the conclusion that the toxin molecules possessed two 

 different affinities, which he described as haptophorous or 

 combining, and toxophorous or poisoning. The former were 

 constant, the latter variable. The deterioration in the 

 strength of the toxic filtrates of bouillon cultures of diph- 

 theria bacilli was shown to depend upon the transformation 

 of the toxin into toxoids which were not poisonous, and 

 was shown to be quite independent of the antitoxin com- 

 bining affinity of the filtrate which remained unaltered. 

 The inevitable interpretation seemed to be the existence 

 in the bouillon of the haptophorous and toxophorous 

 groups described. Similar toxophorous and haptophorous 

 groups were shown to exist in other toxins tetanolysin, 

 by Madsen, venoms, by Myers, and milk-curdling fer- 

 ments by Morgenroth. The neutralizing action of the 

 antibodies produced in the blood of animals immunized to 

 these various substances depends upon the immediate and 

 direct combination or union of haptophorous groups in the 

 antibodies with corresponding haptophorous groups of the 

 respective toxins or active bodies. 



The physiological activities of toxins differ from those of 

 alkaloids and other poisons differ in three fundamentals: 



* The writings of Ehrlich and his associates are so numerous and 

 scattered, and often so fragmentary, that instead of referring to the 

 literature according to the method adopted in other parts of this 

 work, the reader who desires to refer to the original articles can best 

 do so by making use of the following: Ehrlich, "Die Werthbemessung 

 des Diphtheric Heilserums," Klinisches Jahrbuch, 1897; Ehrlich, "Die 

 Konstitution des Diphtheriegiftes," Deutsche med. Woch., 1898 ; "Gesam- 

 melte Arbeiten zur Irnmunitatsforschung," August Hirschwald, Berlin, 

 1904 this work contains the collected papers of Ehrlich and his associ- 

 ates, Aschoff, " Ehrlich's Seitenkettentheorie und ihre Anwendung auf 

 die Kiinst.lichen Immunusirungs-prozesse," Jena, 1902, and the chap- 

 ter upon "Wirkung und Entstehung der Aktiven Stoffe im Serum 

 noch der Seitenkettentheorie," by Ehrlich and Morgenroth in Kolle 

 and Wassermann's "Handbuch der Pathogene Mikroorganismen," 

 Jena, 1904, Gustav Fischer. Readers unacquainted with the German 

 language may find the essential facts in Ehrlich's Croonian Lecture, 

 Proceedings of the Royal Society of London, LXVI, 1900, p. 424, and 

 in Welch's ''Huxley Lecture," Medical News, LXXXI, 1902, 2, p. 721. 



