no Immunity 



and tolerance to usually destructive toxins natural to a few. This 

 toxin-neutralizing or annulling factor cannot be identical with the 

 bacteria-destroying mechanism. Cobbett,* Roux and Martin, f 

 and Bolton J have shown that horses that cannot be supposed ever 

 to have come into contact with diphtheria bacilli, vary considerably 

 in their resistance to diphtheria toxin, and that the serum of the 

 resisting horses contains something that destroys or neutralizes the 

 toxin in vitro, as well as exerts a protective influence upon animals 

 into which it is injected. This substance exerts no inimical action 

 upon the diphtheria bacilli, beyond what a normal serum would do, 

 therefore cannot be alexin, but must be antitoxin. Abel§ found that 

 the blood of healthy men occasionally contained some substance 

 capable of neutralizing diphtheria toxin; Stern found one normal 

 serum capable of protecting against typhoid infection and Met- 

 schnikoff one that protected against cholera infection. Fischel 

 and Wunschheim|| found newly born babies immune against diph- 

 theria, presumably because of the presence of a small quantity of 

 demonstrable protective substance in the blood. These are, 

 however, peculiar and exceptional cases. 



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 con- 

 stant 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 de- 

 scribed 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 



* "Lancet," Aug. s, 1899, 11, p. 532. 



t "Ann. de I'lnst. Pasteur," 1894, viii, p. 615. 



j "Jour, of Experimental Medicine," July, 1896, i, No. S- 



§ "Centralbl. f. Bakt.," etc., 1895, xvii, p. 36. 



II "Zeitschr. fiir Heilkunde," 1895, xvi, p. 429-482. 



**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 consult 

 the original articles can best do so by making use of the following: Ehrlich, 

 "Die Werthbemessung des Diphtherie Heilserums," Klinisches Jahrbuch, 

 1897; Ehrlich, "Die Konstitution des Diphtheriegiftes," Deutsche med. Woch., 

 1898; "Gesammelte Arbeiten zur Immunitatsforschung," August Hirschwald, 

 Berlin, 1904— this work contains the collected papers of Ehrlich and his associates; 

 Aschoff, "Ehrlich's Seitenkettentheorie und ihre Anwendung aut die Kunst- 

 lichen Immunusirungs-prozesse," Jena, 1902, and the chapter upon "Wirkung 

 und Entstehung der Aktiven Stoffe im Serum noch der Seitenkettentheorie," 

 by Ehrlich and Morgenroth in KoUe and Wassermann's " Handbuch der Patho- 

 gene 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, 1900, Lxvi, p. 424, and in 

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



