252 IMMUNOLOGY 



diphtheria toxin there develop toxoids with different affinities 

 for antitoxin and that one of these, which he called protoxoid, has 

 a greater affinity for antitoxin than has toxin. The fraction of 

 toxoid possessing the same affinity as toxin for antitoxin he called 

 syntoxoid. To other toxoids with lesser affinities he gave other 

 names. Thus he built a concept of a toxin spectrum Avhich is exten- 

 sively discussed in his studies (1910). 



He conceived of the union of toxin and antitoxin as resembling 

 the reaction between a strong acid like sulphuric acid and a strong 

 l)ase as, e.g., sodium hydroxide. These react completely in one 

 direction and with only an appreciable degree of reversibility 

 (Wells, 1929). 



Arrhenius and Madsen. — Arrhcnius and IMadsen (1907) 

 studied the reaction between tetanolysin and antitetanolysin and 

 concluded that the reaction between toxin and antitoxin resembled 

 that between a weak acid such as boric and a base such as am- 

 monia. When the latter react an equilibrium is established and 

 there is present a measurable amount of free acid, base and the 

 neutral salt. This theory is apparently accepted by Clenny 

 (1931). 



Bordet's Theory of Adsorption. — The third thcoiy, that of 

 Bordet, assumes that as antitoxin is added to toxin, there is a 

 partial neutralization of each molecule of toxin by antitoxin in- 

 stead of the neutralization of progressively large amounts of the 

 toxin until finally all is neutralized by antitoxin. He does not 

 deny the existence of toxoids but considers that Ehrlich's toxone 

 is merely partially neutralized rather than a separate toxin. In 

 his opinion the union of toxin and antitoxin is an adsorption 

 phenomenon in which the mechanism of union is similar to that 

 in other antigen-antibody reactions. Wells (1929) considers that 

 Bordet's theory comes nearer explaining the ''zone phenomenon" 

 and the "Danysz effect" than either of the other two theories. 



Zone Phenomenon. — The "zone phenomenon" is perliaps best 

 illustrated by the trypanocidal effect of immune serum injected 

 into rats infected with trypanosomes. Taliaferro and Johnson 

 (1926), Johnson (1929) and Coventry (1930) find that if one 

 starts with a dose of immune serum that destroj's the trypano- 

 somes and injects a series of animals with progressively larger 



